ADDENDA.

Page 76.

I have said that crystals of sulphate of magnesia, called by the Spanish inhabitants, madre del sal, are scattered on the borders of the Salinas in Patagonia. By a mistake a wrong bottle was examined; and the crystals, I now find, are the sulphate of soda; but it appears that some sulphate of magnesia is dissolved in the underlying fetid mud.

Page 96.

In enumerating the fossils, which I collected at Bahia Blanca, I mention a tusk like that of a boar, and some very flat grinders. These are now found to belong to the lower jaw of Toxodon Platensis. For an admirable description of this wonderful animal, and likewise of the great fossil (Macrauchenia Patachonica), mentioned at p. 208, which in some respects is allied to the Camelidæ, I must refer to the first part of the Zoology of the Voyage of the Beagle by Mr. Owen.

Page 97.

The remains just referred to, are said to be embedded with existing species of shells. This expression requires some qualification; the details are given in my geological introduction to Mr. Owen’s account of the Fossil Mammalia, above mentioned.

Page 150.

With reference to what I have said, about the bones of horses having been several times brought to this country from North America, with those of the Mastodon, I see Mr. Rogers, in his Report to the British Association (vol. iii., p. 24) says, “It is possible that the horse ought to be added to this list of animals as indigenous to America;” and it is evident from a previous passage, that the bones have been found fossil. Mr. Rogers states, that the remains of two kinds of elephant and three kinds of oxen have been discovered there; as have, on two occasions, parts of the Megatherium. At Big Bone Lick, where the remains of the elephant, mastodon, and ox, are so extraordinarily numerous, the megalonyx has been found; and this is a parallel case to the contemporaneous embedment, in the southern hemisphere, of the mastodon, horse, megatherium, and the other Edentata. The more I reflect on the geographical distribution in the Old and New World of these gigantic mammifers, during the period antecedent to the present, in relation to the existing faunas of North and South America, now so strongly contrasted with each other, the more pregnant with interest the case appears to be. I know of no other instance, in which we can thus almost mark the period of the splitting up of one great region into two well-characterized zoological provinces. With respect to the ancient range of the genus Equus, I may add to what has already been said, that its remains have been found from England in the west, to the Himalaya in the east, (Buckland’s Reliquiæ Diluvianæ, p. 222,) and from the western coast of North America, to the eastern plains of America in the southern hemisphere. We may, therefore, suspect that a very little research would discover the remains of the horse, embedded in the frozen soil of Kamtschatka, with those of the fossil ox and elephant; and thus render complete the evidence, that we there see the ancient, but perhaps temporary line of junction, since interrupted, between the fauna of what we call the New World with that of the Old. But I doubt not, that the snow-clad heights of Chimborazo, Illimani and Aconcagua have seen as many, and as strange forms of animals, pass by and become extinct, as ever did the Alpine pinnacles, or those loftiest ones of the Himalaya.

Page 268.

When contrasting the productions of the eastern coast of South America, with those of the western, and likewise with those of the corresponding parallels of latitude in Europe, I should have added (line 15) after the grape and fig, as flourishing in lat. 41°, the peach, and the nectarine (both of course standards), water and musk melons, batatas dulces (Convolvulus batatas), the olive and the orange; the latter, however, had only been lately introduced, but it promised to succeed well.

Page 272.

I have spoken of the low latitudes in which tropical forms of vegetation are found in the southern hemisphere, and likewise of some mammalia and of birds. With respect to the parrot of the Strait of Magellan, Macquarrie Island in lat. 55° S. and long. 160° E. offers an analogous instance, in possessing a species of this genus. I am, however, now enabled to bring forward a more important observation, as directly bearing on the evidence by which geologists have chiefly judged of the climate of ancient Europe, namely, on the character of the marine productions of the southern hemisphere. In my journal I have remarked that the southern seas teem with life, under innumerable forms; and the truth of this remark is amply attested by the vast herds of great unwieldy seals with which the shores of Patagonia, the Falkland and the Antarctic islands, were, according to the narratives of all the early navigators, almost covered. Having mentioned these facts to Mr. George B. Sowerby, he informs me, that the shells of the southern part of the southern hemisphere have some affinity in general character with those of the intertropical seas, or rather that they are of much larger size and of more vigorous growth than the analogous species (excepting the chitons of California) under corresponding zones in the northern hemisphere. Thus the immense size of the Patellæ, Fissurellæ, Chitons, and Barnacles of the Strait of Magellan, and the large size of the former at the Cape of Good Hope, may be taken as instances. On the east coast of South America (in lat. 39°) three species of Oliva (one of large size), a Voluta (and perhaps a second species), and a Terebra, are amongst the most abundant shells on the mud-banks of Bahia Blanca. Another species of Voluta is found as far south as 45°, and there is some reason to believe, even much further. Oliva, Voluta, and Terebra are amongst the best-characterized tropical forms, that is, both the individuals and species of these genera are extremely abundant in the intertropical seas, whilst they are very rare, or do not exist, on the shores of temperate countries. It is doubtful even if one small species of these three genera, an Oliva, inhabits the southern shores of Europe; whilst in a higher latitude, on the coast of South America, species of all three are the most abundant kinds.

At Bahia Blanca many of these shells are embedded in gravel, and have been raised above the level of the sea. Now let us suppose that the climate of South America and of the surrounding seas were to undergo some change, so as to become in every respect like that of Europe; it can, I think, scarcely be doubted, that the shells of the above-mentioned genera would gradually become extinct, and be replaced by others better adapted to the new climate. What, then, would a geologist say, who entertained the generally-received opinions on the distribution of organic beings in accordance with our knowledge of the northern hemisphere (or, rather, in this imaginary case of both hemispheres), when he found these gravel beds abounding with Olivas, Volutas, and Terebras?—such shells not existing there. We may also suppose that he had discovered that the limits of the more tropical forms, both animal and vegetable, of the productions of the land, had likewise during this former period extended further south: what, then, would he say? Would he not at once infer, with the strongest appearance of truth, that the climate formerly had a more tropical character, properly so called, and therefore had a higher annual mean temperature than at present? Nevertheless, we know such an inference would have been absolutely erroneous. To put the case in another point of view: should a geologist find, in lat. 39°, on the coast of Spain, a tertiary deposit, abounding with Olivas, Volutas, and Terebras; or in lat. 45°, on the coast of France, other beds, containing a large Voluta, and numerous Patellæ, Fissurellæ, Chitons, and Balani, larger and of stronger growth than the existing species, would he be justified, after what is now known, in pronouncing that the climate formerly had a higher mean temperature? I think it may be safely asserted that he would not be so justified, but rather would be bound to search for other evidence. In the actual case of Europe, we have knowledge (as will be shown in a following note⁠[1]⁠) of another element in the problem, namely of the lower descent during former times of the snow-line,—as is inferred from the former low descent of glaciers, on the same mountains, where they now occur only at great heights, and likewise from the congelation during this same period of the soil in a low latitude—and this new element, I believe, gives the key to the solution of the problem, which is, that the climate of Europe was formerly more equable, but so far from being strictly more tropical, that it probably even had a lower mean annual temperature than it now possesses. I need scarcely say that I here refer only to the later tertiary periods: in the more ancient epochs, the plainest analogies tell us of an equatorial climate, whilst on the other hand, we are very far from having the smallest reason to suppose that the snow-line then descended low; and this is the key, as I have called it, to the problem of later times.

Page 282.

With respect to ice transporting fragments of rock in the Antarctic regions, M. Cordier, in his instructions (L’Institut, 1837, p. 283) to the voyage of the Astrolabe and the Zélée, has this passage: “Les relations de l’expédition anglo-américaine de découverte exécutée en 1830, nous ont fait connaître que les plages des Nouvelles-Shetland sont couvertes de grands blocs erratiques formés de granite, et par conséquent d’une nature différente des autres roches du pays. M. James Eights, naturaliste de l’expédition, n’hésite pas à considérer ces blocs comme ayant été apportés par les glaces, qui viennent annuellement s’échouer et se fondre sur les plages dont il s’agit et comme étant les indices de terres inconnues situées plus près du pôle que la terre la Trinité.” I have not been able to find any account of this expedition. Lieutenant Kendall describes (Geograph. Journal, 1830) pinnacles of syenite in Smith’s Island, one of the South Shetland group; so that the inferences regarding the distances, from which the blocks are supposed to have come, probably are erroneous.

In speaking (p. 272) of the rigour of the climate of Deception Island in South Shetland, I might have mentioned that Lieut. Kendall says (Geograph. Journal, 1830, p. 66), that on March the 8th, “We took the hint of the freezing over of the cove (lat. 62° 55′) and effected our retreat.” This is the same as if, in the northern hemisphere, the harbour of Christiansund in Norway, were to freeze on the 8th of September!

Page 285.

I have described the dimensions of the great glacier which in lat. 46° 50′, sends down an arm to Kelly Harbour, and another to a flat swamp; I now find from information communicated to me by Captain FitzRoy, that it must communicate with the channels and bays northward, which extend behind the peninsula of Tres Montes. Aguëros, in giving an account of an expedition of the missionaries (Descripcion Historial de la Provincia de Chiloe, p. 227), says, they encountered in the Laguna de San Rafael (lat. 46° 33′ to 46° 48′) “many icebergs (muchos farallones de nieve), some great, some small, and others middle sized.” This was on the 22d of November, 1778. Captain FitzRoy also tells me, that in the account of another missionary voyage, it is said that the boats had difficulty, on account of the islands of ice, in passing through the Caño de Perdon, a strait connecting the Laguna de San Rafael, with the other bays behind Tres Montes. Transposing in imagination, as I have done at p. 291, the places in the southern hemisphere to corresponding ones in Europe, these facts are the same as if, in a channel of the sea stretching from the Mediterranean between the Alps and the Jura, a boat should encounter in the latitude of the lake of Geneva, and on the 22d of June, (but not on one occasion only,) so many icebergs, and of such dimensions, that the historian of the voyage should describe them as being “some great, some small, and others middle sized”!

Having insisted so strongly, in this part of my Journal, that it is in the southern hemisphere, where tropical forms encroach on the temperate zones, that solid glaciers descend to the sea in low latitudes; I might have added that it is in this same hemisphere, that the icebergs, which have been formed in the Polar Regions, are drifted furthest from their birthplace. Horsburgh (Philosoph. Transact., 1830) describes several great icebergs seen by a ship, in her passage to India, in 35° 50′ S.: that is, far to the northward of the latitude, where tree-ferns, arborescent grasses, parasitical orchideous plants, and even palm-trees grow; and within sixty miles of the land, where the rhinoceros, elephant, hippopotamus, lion, and hyena, are very numerous.

Page 289.

Until lately I was not aware that there were sufficient data to speak with some precision of the southern limits of erratic blocks in the northern half of the New World. In Canada, and in the northern parts of the United States, innumerable great scattered fragments of rocks have been described by Bayfield, Bigsly, Hitchcock, and others. In parts of Massachusetts, according to Professor Hitchcock (Report on the Geology of), boulders seem to cover the whole face of the country. Further southward we hear from Mr. Rogers (Report to Brit. Assoc., vol. iii.) that boulders are common over the great valley which crosses Pennsylvania, Maryland, and Virginia (lat. 36° 30′ to 42°): and likewise in the states of Ohio, Kentucky, and Indiana, which are in nearly the same latitude. Mr. Rogers having described some blocks of sandstone at Washington and on the Susquehanna, which must have come from some distance northward, adds that “Drake in his picture of Cincinnati (39° 10′) mentions large masses of granite in that part of the Ohio, resting on the ordinary finer diluvium. The nearest granite to the north is at least one hundred leagues distant; while no primary rock occurs south or east, within even a much greater limit.” He then proceeds, “We are reminded here of the great detached blocks, which strew the plains of northern Europe, and the explanation suggested, that they have been carried there upon floating ice;” and concludes with the important remark, that Mr. Conrad, who has explored the state of Alabama (30° to 35°) was never once able to perceive a boulder upon its surface. It would hence appear that 36° 30′ is the southern limit of the dispersion of erratic blocks in the United States; and these are spoken of, as having come from the north. Therefore, there is no occasion to suppose that the ice, in which by the theory they are believed to have been embedded, was formed in so low a latitude as that here mentioned; and at present, in the southern hemisphere, icebergs are drifted to latitudes, though not formed in them, nearer the tropic than 36° 30′. In Europe I cannot hear of erratic blocks having been found further south than the southern flanks of the Alps, in lat. 45°; and Humboldt has said (see Cuvier’s Theory of the Earth, translated by Professor Jameson, p. 346) that they do not occur in Lombardy. I may here remark, that care should be taken to separate the phenomenon of great angular blocks, from that of rounded ones, although of considerable size; for torrents, and more especially the waves of the sea, during its slow oscillation of level, are agents sufficiently powerful to produce great effects. The lowest latitude in South America, in which I found large angular fragments, which must have been transported by ice there formed, or by some unknown means, was in latitude 41°. But as I did not examine the country immediately north of it, I am not prepared to say that this is their extreme limit; but between latitude 27° and 33°, I found no appearance, on either side of the Cordillera, which indicated a power of transportation of the kind required to remove boulders from a distance. Thus, we find that the limit of their dispersion in the two Americas is nearly the same; although they approach the warmer zones rather more closely in the northern than in the southern division of the continent, and in both, probably, more so than in Europe.

In the note, in which I have considered the apparent exceptions to the law, that erratic boulders are not found in the intertropical regions, I have said that the internal evidence of the Macao case led me to doubt its reality, and I now find it is distinctly stated by M. Chevalier that the rounded blocks result from the secular disintegration of the fundamental rock (L’Institut, 1838, p. 151—Analysis of the Voyage of the Bonite). I may here add, that M. Puillon Boblaye, in his description of Bone and Constantine on the northern coast of Africa (L’Institut, 1838, p. 248), says, “Je n’ai rien vu que pût indiquer le phénomène des blocs erratiques.” My statement that erratic boulders are not found in Australia, is fully borne out by information communicated to me by Major Mitchell, who, in his repeated expeditions, has traversed so much of the south-east division of that continent. With the several facts given here and in the Journal (p. 289), I can scarcely doubt that the law of the distribution of erratic blocks is finally determined; and it is needless to specify the great, not to say conclusive, importance of this law on the theory of the means of their transportation,—a problem which has so long perplexed geologists.

Page 294.

In my discussion on the climate of the southern hemisphere, I have shown that a low altitude of the line of perpetual snow, and consequently the descent of glaciers to the level of the sea in latitudes relatively low to what occurs in the northern hemisphere, and likewise the perpetual congelation of the soil a little beneath the surface in countries without the frigid zone, are the results of a climate which appears favourable to the passage of tropical forms beyond their proper limits, and to a vigorous native vegetation. The climate is one of an equable nature; and this must, to a considerable degree, be the effect of the great area of ocean compared with the land of the southern hemisphere. In the northern hemisphere we have proofs, that the productions both of the land and water, during the period antecedent to the present, had a more tropical character than they now have, and there is, also, a high degree of probability that the proportional area of water was much greater.

If then we judge from the analogy of the southern hemisphere, the first and simple inference from these facts, is, that the temperature of Europe was formerly more equable, though perhaps with a lower mean, than it now is. It may be asked, as a test of this inference, did the snow-line formerly descend lower than it now does? Was the soil formerly frozen a little beneath the surface in a low latitude? The congealed carcasses of the great Pachydermata of Siberia answer the second question; and in my journal, I have indirectly considered the first one as answered, by the fact of the many erratic boulders of Europe having travelled from mountains, situated in regions where great bodies of ice do not at present descend to the level of the sea. For on the theory that these boulders were transported by icebergs from glaciers, which formerly descended into the sea in latitudes where perpetual snow is not now found, or if so, only at great heights, the problem receives so simple a solution, that I did not hesitate, having the other data, to assume, that the snow-line in Europe formerly did descend much lower than it does at present. But, had I studied my subject more attentively, I might have taken a higher ground: in a note, indeed (p. 294), I have stated that according to Professor Esmark, it is certain, that the glaciers of Norway formerly descended to a lower level; and I now found that some time since, Messrs. Venetz and Charpentier, and more lately M. Agassiz, have incontestably shown, from the presence of glacier-dikes or moraines, and from the polished and scratched surface of the rocks, that in the Alps enormous bodies of ice formerly descended to the borders even of the lake of Geneva, and therefore much lower than the line of present lowest descent.⁠[2] With these several facts it might have been boldly asserted, that the climate of Europe formerly was like that of the southern hemisphere as it now is; and consequently, as we know, that the sea within recent tertiary periods stood at a higher level over a large portion of our continent, it might have been affirmed, had there been no record of the existence of erratic blocks on this side of the globe, that it would be an anomaly, difficult of explanation, should there not be found around the eminences of central and northern Europe great unrolled fragments, scattered at long distances from, their parent sources, and often separated from them by profound valleys.

M. Agassiz has lately (Address to the Helvetic Society, July 1837, translated in Jameson’s New Philosophical Journal, vol. xxiii., p. 364, and in several communications in the French periodical L’Institut) written on the subject of the glaciers and boulders of the Alps. He clearly proves, as it appears to me, that the presence of the boulders on the Jura cannot be explained by any debacle, or by the power of ancient glaciers driving before them moraines, or by the subsequent elevation of the surface on which the boulders now lie. M. Agassiz also denies that they were transported by floating ice, but he does not fully state his objections to this theory; nor does he oppose it, by the argument of the apparent anomaly of a low descent of glaciers, with the generally-received opinion of the more tropical character of the productions of the antecedent periods,—which was philosophical, until the effects of a temperate and equable climate were considered.⁠[3] On the contrary, he assumes that, during the gradual cooling of the earth, there have been periods of excessive refrigeration. It is needless to state that such an hypothesis is not supported by a single fact—without, indeed, the assumed sudden renewal of life on the surface of the world at successive periods be considered such. During this imagined period of excessive refrigeration, the Alps and the greater part of Europe, and even of Asia, are supposed to have been covered by one immense sheet of ice, and during the assumed sudden elevation of the Alps, fragments of rocks are supposed to have been shot over the frozen surface, and, when the ice melted, to have dropped on the surface where they now lie. M. Agassiz considers that this view explains the position of the boulders on pinnacles, and their absence in the valleys. I confess I should have thought, after the flexure and elevation of the ice, these would have been the least probable situations: but neither this, or some other facts (p. 381), are quite intelligible to me from the briefness, with which they are alluded to. M. Agassiz says (p. 375), “The erratic blocks of the Jura every where repose on polished surfaces, all those at least which have not been carried beyond the crest of our mountains, and which have not fallen to the bottom of our longitudinal valleys, as may be seen throughout the valleys of the Creux du Vent. But they do not repose immediately upon these polished surfaces. Wherever the rounded pebbles which accompany the great blocks have not been removed by subsequent influences, it is remarked that small blocks, in other words pebbles of different sizes, form a bed of some inches, and sometimes even of many feet, upon which the great angular blocks repose. These pebbles are also much rounded, even polished, and are heaped up in such a way that the larger are above the smaller, and that the last often pass below into a fine sand, lying immediately over the polished surfaces. This order of superposition, which is constant, is opposed to all idea of a transport by currents; for in this latter case the order of the superposition of the pebbles would have been precisely reversed.” Further on (p. 379) he remarks that the action of the glaciers is immense; “for these masses, continually moving upon each other, and on the surface, bruise and grind down every thing moveable, and polish the solid surfaces on which they repose; at the same time that they push before them all that they encounter, with a force which is irresistible. It is to these movements (of the great stratum of ice) we must attribute the strange superposition of the rolled pebbles, and of the sand, which immediately reposes upon the polished surfaces; and it is unquestionably to the grating of this sand upon these surfaces that the fine lines which we find (previously compared to the scratches made by a diamond on glass) are owing, and which would never have existed, if the sand had been acted upon by a current of water.” Now it may be demanded, by what possible means can such violent action arrange the large pebbles above the smaller ones, and these again above the sand? The fact appears to me utterly inexplicable on this view. Again it is said, that the surface of the rock is marked by furrows and gibbosities, as well as by scratches, and that these “never follow the direction of the slope of the mountain, but are oblique and longitudinal (that is, in the line of the mountain, and therefore nearly horizontal), a direction which excludes every idea of a stream of water being the cause of these erosions.” What explanation will it be believed is offered for this fact?—It is, that the fine lines and furrows “must have resulted from the much greater facility which the ice had in dilating itself in the direction of the great Swiss valley, than transversely, confined as it were between the Jura and the Alps.”!

I will now endeavour to show how far these very curious facts, which we owe to M. Agassiz’s observation, can be explained by the theory of floating ice: and the theory, I may add, if applicable to this case, solves that which presents far greater difficulties, than any other of the kind in Europe. I should first state that I make two assumptions, and if these be rejected, the theory is not applicable to the case of the erratic blocks of the Alps:—first, that an arm of the sea extended between the Jura and the Alps, during that period in which, as I have before shown, it is probable, that the proportional area of water in Europe was greater, and certain, that the productions of the land and water had a more tropical character, at the same time that the snow-line descended lower. The age of the Molasse, which occupies this area, between the Jura and Alps, has not been accurately determined; but it is supposed to be miocene, and is said to contain leaves of the Chamærops, a genus of palms, at present found further from the equator than any other kind. It is not, however, evident that the Molasse was deposited by the sea during the latest period, when it occupied a confined limit between the Alps and Jura; but even if this should be found to be the case, it would be rash in any one positively to conclude that glaciers could not have descended to the shores of a sea, on which the Chamærops flourished, after that we know they descend in the southern hemisphere so near the limits of several tropical forms.

My second assumption is, that the elevation of this much of Switzerland, whenever it took place, was slow and gradual: this is supported by the strongest analogies of South America, Scandinavia, and other parts of the world; whilst on the other hand, the assumption that it had been sudden, would be unsupported by a single ascertained fact in nature. Now, as the numerous masses of ice, which fall from the glaciers at the head of the sounds on the South American coast, are slowly drifted outwards (owing to the fresh water flowing in from the foot of the glaciers), and in the more open channels are left to be acted on by the winds and currents; so must it have been with the icebergs from the glaciers of the Alps, situated in the same latitude, and under similar conditions. These icebergs would in most cases be driven on some part of the surrounding shore; but from floating deep they would ground a little way from the beach, and then being packed together, and driven to and fro, as the winds changed, and as the tides rose and fell, would they not, like a glacier on the land, though in a lesser degree, “bruise and grind down every thing and polish the solid surface, on which they reposed?” In the rapids of the North American rivers, over which large bodies of ice are driven, carrying with them pebbles and fragments of rocks, I am informed by Dr. Richardson, that the primitive rocks are scooped and hollowed, and have their surfaces polished and glossy. Dr. Richardson, however, is not prepared to say, whether this is caused by the passage of the ice or of the pebbles.⁠[4] Although the icebergs might be drifted from side to side of the sound, if they were moved after having grounded, it would be along the shore by the set of the currents or wind, and perhaps slightly up and down by the tidal changes. Would not the necessary effect of this be, that the scratches formed by the sand grating between the rocks and the bottom of the icebergs should be, with some irregularities, longitudinal, or (from the effect of the tidal movement) oblique? And as the mountains slowly emerged during ages, every part would be thus acted on; and consequently the whole surface would be marked by longitudinal scratches.

The icebergs on the South American coast sometimes transport angular fragments of rock, to the distance of many miles from the glacier whence they were detached; and as the winds and currents generally have sufficient steadiness to drive any floating object soon on shore, (as is known to be the case with a capsized boat, a barrel, or floating carcass, &c.), so the blocks of rock would be generally⁠[5] landed on the shores of the channels between the Alpine ranges, and not dropped in the intervening spaces. If any pointed rock came so near the surface that a floating mass of ice, thus charged, grounded on it, the block would, when the ice melted, be there left. But it may be asked, would the blocks usually be deposited on the bare surface of the rocky bottom off the shore, or on an intervening layer of gravel or sediment? From what I have observed when passing in boats through the channels of Tierra del Fuego, and from frequent examinations of the armings of the lead used in sounding, I feel nearly sure that absolutely bare submarine rock is not very common. Moreover, where matter is depositing near a shore, the finer the particles are, the further they are drifted: in approaching a coast I have actually traced every step in the series, from the finest sand to large pebbles. But as the land in any case is slowly elevated, the same forces which carried the large pebbles to a certain distance from the beach, and the smaller ones to a still further distance, will, after each little elevation, carry them somewhat further:—a layer of little pebbles thus covering the sand, and a layer of large pebbles the smaller ones. Hence, when the part near the shore is converted into dry land, a section of the bed which was originally the bottom of the sea will necessarily show solid rock covered by sand, this by fine pebbles, and these again by others, gradually increasing in size. Such then, I conclude, must have been the nature of the sub-littoral deposits of the Alps, during their assumed slow elevation. Finally, as icebergs of large size would seldom be driven up on the beach of a sheet of water, if, like the channel between the Jura and the Alps, it were protected from the open sea, any fragments of rock transported by them would have been dropped some way outside, and therefore when upraised with the whole country, they would be found in most cases reposing on beds (where the loose matter had not been subsequently removed), characterized by the order of superposition just described.

Such is the explanation I would suggest of the very curious facts observed by M. Agassiz. I make no assumptions which are not supported by strong analogies and the foundation of the theory—namely, a change of climate of a peculiar kind—can be shown by reasoning, independent of the existence of erratic blocks, to be probable in a high degree: whether this is the case with the theory of M. Agassiz, I leave the reader to decide.

Having said thus much on the scratched rocks of the Alps, I am tempted to make a few remarks on those of Scotland, described by Sir James Hall⁠[6] in his celebrated paper (Edinburgh Phil. Transact., vol. vii.) on the Revolutions of the Earth’s Surface:—a case which has always appeared to me to be the strongest ever adduced in favour of the theory of an overwhelming debacle having rushed, at least in that country, over hill and valley. The furrows and scratches in the same district are parallel to each other, and hence run in the same direction:—thus, near Edinburgh, they extend in a line a little north of west and south of east, that is parallel to the valley of the estuary; but both to the eastward and westward they deviate from this line by more than half a right angle; and on the south-west part of Scotland they have no uniform direction. In the north of Scotland, however, near Brora, Mr. Murchison (Geolog. Transact. 2d Series, vol. ii., p. 357) found the hills marked in parallel lines, directed north-west and south-east. The furrows and scratches near Edinburgh seem generally to traverse the less inclined surfaces, but Sir James, speaking of one part, says “the perpendicular face as well as the rest is covered with lines, which are horizontal, or nearly so.” In these respects the case appears very similar to that of the Alps: the rocks, however, are not polished;⁠[7] but this may be owing to their nature, sandstone and trap, and not to any difference in the cause; for Dr. Richardson tells me that in the same rivers in North America, in which the granitic rocks are much polished, those of laminated limestone are not at all so. Near Edinburgh, where the lines extend west and east, the western face of the hills (of which the highest mentioned is four hundred and seventy feet above the sea) is chiefly marked, whilst on the opposite or protected side, a long tail of (so called) diluvium extends, which consists of blue clay, with large erratic boulders embedded in it. These boulders, as I am informed by Mr. James Hall, and by Mr. Smith of Jordanhill, are themselves marked with parallel lines, having one direction, which shows that they were held fast whilst drifted across the country, and not rolled over and over, like a pebble in a stream. It is admitted by all that the grooves on the solid rock were formed by the passage of these boulders over it. Although the minor inequalities of the surface of the land appear to have had no influence whatever on the action which produced the scratches, yet the larger features, as the general bearing of the main valleys, appear to have determined their direction. Sir James distinctly states that the scoopings and furrows have precisely that form which the long action of torrents tends to produce on a solid rock; but he adds, and I believe most truly, that the furrowed surface produced by such means is smooth, and not deeply scored and scratched. It is indeed utterly inconceivable that large stones should be carried along as if “independently of their gravity” by any ordinary means, with such velocity, as to mark with horizontal lines the perpendicular face of a rock. From these facts,—from the presence of great erratic blocks, from the steepness of one face of the grooved hills, and the tail of sediment stretching out from the other, Sir James Hall, having in his mind the recorded cases of the great waves consequent on earthquakes, inferred that a vast deluge had burst over the country from the westward.

M. Brongniart, and lately M. Sefström (L’Institut, February 22d, 1837), have described phenomena in Sweden almost identical with those of Scotland. The rocks are there grooved and scratched,⁠[8] even to the height of 1500 feet, in north and south lines, parallel to the valley of the Baltic and of the Gulf of Bothnia; but they are considerably deflected by the larger inequalities of surface. The north side of the hills are most affected, whilst from the southern side, long ridges, called oasars, stretch out; they are composed of sand and water-worn materials, and appear to be similar, but on a much larger scale, to the tails of diluvium in Scotland. In Sweden, however, the erratic blocks always lie on the surface of these ridges, and are not embedded within them: but M. Sefström says, that at the time when the grooves were formed, enormous masses of rock were torn from the mountains. In the United States, the phenomenon of the grooved rocks appears to be developed in an extraordinary manner. Professor Hitchcock (Report on the Geolog. of Massachusetts, p. 167) describes a tract about two hundred miles in width, over which nearly all the bare rock on the hills, even to the height of three thousand feet, is scored by parallel lines. In some parts boulders, weighing from fifty to one hundred tons, are yet lying on the surfaces, which bear the marks of their passage. The furrows are generally directed a little west of north, but in the western part of Massachusetts, and in the eastern of New York, they extend in a north-west and south-east line, and in one part even to W. 20° N. M. Sefström and Professor Hitchcock explain these appearances in their respective countries by the same agency, as Sir James Hall does in Scotland.

The theory of a great debacle is in these cases based on the united presence of erratic boulders, ridges of water-worn materials, forming tails to scarped hills, and parallel furrows and scratches on the surface of the rocks. 1st. With respect to the boulders, it would be superfluous to repeat the arguments in favour of the idea of their transportation by ice: and in the case of Sweden, it would be pre-eminently superfluous, as we know (see Lyell on the Rising of the Land in Sweden, Phil. Transact., 1835) that blocks are there transported yearly by this means. 2d. Every one who has examined a great estuary, or a channel where the tides run strongly, is aware that linear banks are formed behind any obstacle. Therefore these tails of diluvium might have been formed, as far as regards their external form, by ordinary means; and with respect to their internal structure, which appears extremely irregular, and without any stratification, it must be difficult for any one to speak with certainty, until the joint effects of ice transporting coarse fragments and gentle currents of water, fine mud, are better known. Mr. Lyell, indeed (Phil. Transact., 1835, p. 15) has advanced strong reasons, showing from the structure and composition of the oasars that they could not have been formed by any sudden debacle. Whilst such linear banks were depositing on one side of the hills, the other, or exposed front, would almost necessarily become scarped. 3d. We have the admission of Sir James Hall, that the scoopings and grooves resemble those produced by the slow action of running water: therefore the scratches appear to be the only part of the phenomenon which remains unexplained.

In the Alps, we are told, that scratches are formed on rocks by glaciers grinding over them. According to the theory of floating ice, we have evidence in the erratic blocks near Edinburgh, that ice was formerly in action there; and, from the analogies given in this volume, it might well have been so, since the scene of supposed action lies two degrees nearer the Pole than Georgia, in the southern ocean, “almost wholly covered with everlasting snow.” What then would be the effect of the tides and gales of wind, driving packed icebergs with irresistible force, through channels, and over rocky shoals;—each part of the surface being exposed for centuries, as the country was elevated, to this action? Would not the fragments of rock embedded in the ice grate in a direct path over the surface, regardless of minor inequalities? and would not the fragments themselves be grooved and scored in one direction? Can we for one moment believe it possible that boulders, either in water or in the thickest mud, could be driven over a rugged surface, or along a perpendicular face of solid rock, with such enormous velocity as with their points to groove and scratch it, and nevertheless not to be rolled over and over, like a stone descending a mountain, but to be marked with parallel lines of abrasion, equally with the fixed, underlying mass? It appears to me that we assuredly can make no such admission. Travellers in the Arctic regions tell us that the drift-ice, with its irresistible power, can force up the gravel and sand into mounds (see Geograph. Journal, vol. viii., p. 221), and drive before it great boulders, and even ships, and masses of ice, high and dry on the beach. What then would be the effect of a few pebbles, or a single fragment, between such masses of ice and a steep coast-wall of rock? Would not scratches “horizontal, or nearly so” be formed, “indicating (to use Sir James Hall’s words) that grinders had been pressed against the rock;” as if “independently of their gravity”?

In this explanation only veræ causæ are introduced, and reasons can be assigned, for the belief that these causes have been in action in these districts. On the theory of debacles, it still remains to be proved that rocks can be thus scooped and furrowed, or hills scarped; although I am far from affirming they cannot,—and scratched, I presume, they certainly would be. With respect to Sweden, where the land is now rising, and where ice even still is a transporting agent, it is undoubtedly the part of the geologist, to endeavour by long and laborious research to account for the phenomena by these real agencies. For to introduce, before it is absolutely forced on us, the hypothesis of a deluge of mud and stones, fifteen hundred feet deep in Sweden, or three thousand in North America, which rushing over the country, rounded the northern fronts of the hills, and rolling by their eastern and western flanks, left them marked with oblique furrows, is to violate, as it appears to me, every rule of inductive philosophy.

Page 297.

With reference to the embedment of the Siberian animals with their flesh, I have mentioned in a note, the case of ice described as rising from the bottom of the sea, off the coast of Greenland. Messrs. Dease and Simpson, during their late memorable journey along the shores of the Arctic ocean, speaking of one part (Geograph. Journal, vol. viii., p. 218) say, “The ice lay much closer here; and numerous masses adhered to the bottom, under the water, which obliged us to search a passage out from the shore.” Further on (p. 220) they say, “But nowhere had the thaw penetrated more than two inches beneath the surface (of the land), while under water along the shore, the bottom was still impenetrably frozen.” This was on the second of August. It should, however, be observed, that the sea along this part of the American coast is extremely shallow.

Page 321.

I have given my reasons for believing that the temperature of the mineral springs of Cauquenes, was permanently changed by the earthquake of 1822. This inference is altogether false, for I find that Schmidtmeyer, in his Travels in Chile during the years 1820 and 1821, says (p. 311) that the temperature of the different springs was 83°, 103°, 106°, 112°, 117° and 118° of Fahrenheit. Now Mr. Caldcleugh says, after the earthquake of February, 1835, the temperature fell from 118° to 92°. Previously, therefore, to this shock, it had regained the temperature which it had in 1820.

Page 377.

When I offered my views on the cause of the great waves, which follow earthquakes on certain coasts, I was not aware of the paper on this subject by Sir James Hall in the Edinburgh Royal Transactions, vol. vii., p. 154. I cannot, however, perceive the necessity of a sudden elevation of the bottom, to produce the observed effects, as supposed by that distinguished philosopher. Having read the abstract of a Notice on the Resistance of Water, by Mr. Russell, I perceive the subject is far more intricate, than I was at the time aware.

Page 381.

I have said that during the few months subsequently to the great shock of February, 1835, at Concepcion, upwards of three hundred tremours were felt, but I should have said, within twelve days. (See Geograph. Journal, vol. vi., p. 322. Sketch of Surveying Voyage of the Adventure and Beagle, by Captain FitzRoy). From some additional information which I have met with since finishing this chapter, I find the train of volcanic phenomena, which followed this earthquake, affected a larger area than that mentioned (seven hundred by four hundred miles), and affected it in a manner which gives great additional weight to the argument that South America is in that part a mere crust resting over a sheet of fluid rock; and likewise to the generalization that the action of volcanoes, and the permanent elevation of the land (and consequently, as I believe, the elevation of mountain chains) are parts of the same phenomenon, and due to the same cause.

Page 446.

When I put together the few and exceedingly imperfect remarks on the subject of Miasmata, I did not know of Dr. Ferguson’s remarkable dissertation—the result of his investigations in Holland, Spain, Portugal, and the West Indies—on the Nature and History of Marsh Poison (Edinburgh Royal Transact., vol. ix., p. 273). He there clearly proves the fact, which had struck me with so much surprise, namely, that the driest districts, which, according to common notions, would be considered as the most healthy, are often singularly the contrary. In his concluding remarks, Dr. Ferguson says (p. 290), “One only condition, then, seems to be indispensable to the production of the marsh poison, on all surfaces capable of absorption, and that is the paucity of water, where it has previously or recently abounded. To this there is no exception in climates of high temperature; and from thence we may justly infer, that the poison is produced at a highly advanced stage of the drying process.” And, from facts previously stated, it would appear that even in barren hilly countries, the banks of mountain torrents, which had been overflowed, sometimes became extremely insalubrious. In another place, Dr. Ferguson says, “It is from these (the dried and half-dried margins of lakes and marshes) that the poison uniformly emanates, and never from the body of the lake or pool; and I think it may be fairly presumed, that water, as long as it can preserve the figure of its particles above the surface, is innoxious, and that it must first be absorbed into the soil, and disappear from the eye, before it can produce any mischievous effects. Whoever in malarious countries waits for the evidence of putrefaction will, in all the most dangerous places, wait too long, as every one can testify who has seen pestilence teem forth, to the paralyzation of armies,—from the bare barren sands of the Alentejo in Portugal, the arid burnt plains of Estremadura in Spain, and the recently flooded table-lands of Barbadoes.” I cannot forbear quoting here a remarkable fact, mentioned by Humboldt, though interpreted in a different manner by that illustrious traveller. Speaking of the intermittent fevers which are so common near the great cataracts, or raudales, of the Orinoko, he says (Pers. Nar., vol. v., p. 17) the causes “are violent heats, joined with the excessive humidity of the air, bad nutriment, and, if we may believe the natives (as well as the missionaries), the pestilent exhalations that arise from the bare rocks of the raudales.” Further on (p. 85), he says, “many examples are adduced of persons, who having passed the night on these black and naked rocks, have awakened in the morning with a strong paroxysm of fever.” Humboldt thinks that these cases may be explained by the effect produced on the body by the high temperature, which the black rocks, coated with a layer of the oxides of manganese and iron, retain during the night. But it appears to me that the relation is too remarkable to be thus explained, between this fact and those mentioned by Dr. Ferguson, in which the desiccation of nearly bare rock in Spain, and of a very thin bed of earth overlying dry coral rock in the West Indies, has given rise to the most pestiferous exhalations.

Page 461.

The sixth bird, mentioned as an inhabitant of the Galapagos, Mr. Gould now finds is not like the rest, peculiar to these islands, but is a known North American species of Ammodramus.

Page 465.

I have given my reason for believing that the Testudo, inappropriately called Indicus, is an aboriginal species of the Galapagos. I now find (Kerr’s Voyages, vol. x., p. 373) that as far back as 1708, Woods, Rogers, and Courtney, in their voyage round the world, speaking of the tortoises of these islands, say that it is the opinion of the Spaniards that there is no other in these seas, except at the Galapagos: it is, however, then added, that they are common in Brazil,—a mistake which may be attributed to two different species not having been distinguished. It has been said that the bones of Testudo Indicus were found in numbers in the Isle of France, with some fragments of those of the Dodo; but M. Bibron—one of the best authorities in Europe on reptiles—informs me that he has reason to believe that a second species has been confounded under this name.

In the same page I remark that there is every reason for believing that several of the islands possess their own peculiar varieties or species of tortoise, but that my specimens were too small to decide this question. M. Bibron now informs me, that he has seen full-grown animals, brought from this Archipelago, which he considers undoubtedly to be distinct species. At p. 467, I have observed that the specimens of the Amblyrhyncus cristatus—that extraordinary marine herbivorous lizard—were larger from Albemarle, than from any other island. In this case, also, M. Bibron tells me, he has seen what he considers two species of the aquatic Amblyrhyncus, besides the terrestrial species. Doubtless the several islands have their own representatives of the Amblyrhyncus, like they have of some of the birds, and of the tortoises. With respect to the plants from this Archipelago, Professor Henslow writes to me, that although he has not yet examined them attentively, he finds that “there are several instances of distinct species of the same genus, sent from one island only: that is, whilst the genus is common to two or three islands, the species are often different in the different islands. In some cases the species seem to run very close to each other, but are, I believe, distinct.” I may observe that, from my ignorance of botany, I collected more blindly in this department of natural history than in any other; so that certainly it was not intentionally that I brought the different species from different islands. If, indeed, I at all noticed their resemblance, I probably collected the second and third species as duplicate specimens of the first. It is useless to repeat here my regrets at not having procured a perfect series in every order of nature from the several islands: my excuse must be, the entire novelty of the fact, that islands in sight of each other should be characterized by peculiar faunas: I ought, perhaps, rather to think it fortunate, that sufficient materials were obtained to establish so remarkable a circumstance in the geographical distribution of organic beings, although they are insufficient to determine to what extent the fact holds good.

Page 477.

To the two cases of land-birds being extremely tame in islands only lately inhabited by man, I might have added Tristan da Acunha. Captain D. Carmichael (Linn. Transact., vol. xii., p. 496), speaking of the thrush and bunting—the only true land-birds—says, “they fly about the cantonment, and are so tame as to suffer themselves to be caught with a hand-net.”

Page 552.

One of the species of Millepora, which is mentioned as having the property of stinging, is the M. complanata; and the other, I believe, is M. alcicornis. In the Voyage of the Astrolabe (vol. iv., p. 19), an Actinia is said to have this property, and even to infect the water, which it squirts from its mouth. A flexible coralline, allied to Sertularia, was observed (p. 337) at New Ireland to have the same stinging power.

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