Art. I. Hints on some of the Outlines of Geological Arrangement, with particular Reference to the System of Werner.

Art. I. Hints on some of the Outlines of Geological Arrangement, with particular Reference to the System of Werner, in a letter to the Editor, from William Maclure, Esq. dated Paris, 22d August, 1818.

INTRODUCTORY REMARKS.

Some years since, during Mr. Maclure's geological survey of the United States, the editor had the pleasure of passing a few days, in company with that gentleman, in exploring the geology of the vicinity of New-Haven. Near that town, junctions, on an extensive scale, between widely different formations, are to be observed. A radius of ten miles, with New-Haven for a centre, will describe a circle within which the geological student may find (with the exception of formations, unquestionably volcanic) most of the important rocks of the globe, and a radius of even six or seven miles will include the greater number of these. At, and near the terminations of the primitive ranges, there are rocks which appear to have, in a high degree, the characters of the transition class. Among them is the beautiful green marble of the Milford Hills, seven miles from New-Haven. Mr. Maclure visited that district, and even suggested the first hint which afterward led to the discovery of the marble. Doubts being entertained concerning some of the geological relations of those rocks, a letter was addressed to Mr. Maclure (then in Philadelphia) on the subject. His answer is subjoined.

In giving it to the public, the editor takes a liberty which he hopes the respectable author will pardon, because his production, although evidently never intended for the public eye, contains statements and opinions of no small importance to the young geologist, especially of this country.

Geology, at the present day, means not a merely theoretical and usually a visionary and baseless speculation, concerning the origin of the globe; but, on the contrary, the result of actual examination into the nature, structure, and arrangement of the materials of which it is composed. It is therefore obvious, that the opinions of those men, who, with competent talent and science, have, with a direct reference to this subject, explored many countries, and visited different continents, are entitled to pre-eminent respect. Saussure, by his scientific journeys among the Alps, (although a limited district) has given deserved celebrity to his own name, and, if it were possible, has thrown an additional charm of attraction over those romantic and sublime regions. Dolomieu has made us familiar with the productions and phenomena of volcanoes, those awful and mysterious laboratories of subterranean fire. Humboldt has surveyed the sublimest peaks of both continents, and examined the structure of the globe amidst the valleys of Mexico and the snows of Chimborazo and Pinchinca; and Werner, with opportunities much more limited, (confined indeed to his native country, Saxony) but with astonishing sagacity and perseverance, deduced from what he saw, a classification of the rocks of our globe, which, although not perfect, has done immense service to the science of Geology. In this distinguished group (to which other important names might be added) Mr. Maclure has unquestionably a right to be placed. Few men have seen so much of the structure of our globe, and few have done so much with such small pretensions. His work on American Geology is noticed with becoming respect even in Edinburgh,[28] that focus of geological science. His opinions on some of the more obscure and doubtful parts of the Wernerian geology are worthy of peculiar consideration; for they are founded on a course of observations vastly more extensive than Werner ever had it in his power to make. The name of Werner will always be venerated as long as geological science shall be cultivated, for geology owes more to him than to any other man; but his pupils should not now demand that implicit and unqualified adoption of ALL his opinions, which will allow no other question to be raised, than what Werner taught or believed.

With these explanatory remarks, the following extract of Mr. Maclure's letter is now subjoined:

DEAR SIR,

Your letter of the 26th June came just as I was embarking for Europe. The information it requires concerning the primitive trap and flint slate, the transition and secondary rocks, &c. &c. is difficult to give without the aid of specimens, and frequently requires the examination of the relative position of the strata before any correct idea can be formed. I will, however, endeavour to give you the little my experience has brought me acquainted with.

Following the nomenclature of Werner, I have given a list of his rocks; but in describing them there are many of his names which I do not use; because I never met with them. Primitive trap is one instance—I do not use trap as a substantive, except in describing that kind of trap which Werner calls the newest flætz trap, the nearest to which is your trap,[29] which covers the oldest red sandstone.

The primitive flint slate is in the same predicament. I have always found it on the borders of the transition, between it and the secondary.

Primitive gypsum I have not found.

What Werner calls primitive trap may perhaps be compact hornblende, or perhaps the newest flætz trap, when it happens to cover the primitive; for, this species of trap, like the currents of lava, covers indiscriminately all classes of rocks, and is one reason why I consider it as the remains of ancient lava.

Transition trap is a rock that I have not met with, and may perhaps be a part of the flætz trap that happened to cover the transition, without any immediate connexion, but like a current of lava, overlying all the classes of rocks it meets with. This misapplication of names naturally arises from the system of neptunian origin, on which the nomenclature of Werner is founded.

Greywake and greywake slate are aggregates of rounded particles of rocks, evidently the detritus of more ancient formations, and differ from the aggregates of pudding and sandstone of the secondary class, in the following properties, viz.

The aggregates of transition are harder and much more compact, than the secondary; they are also cemented by argil, taking a slaty form.

This cement is in much greater quantity, in proportion to the particles cemented, and has the appearance as if the cement at the time of formation, had a consistence sufficient to prevent the particles from touching each other.

They have, in common with all the transition rocks, a regular and uniform dip from the horizon, from 10 to 40 degrees; and sometimes more. This is perhaps the strongest mark of distinction which separates them from the secondary, which are horizontal, or follow the inequalities of the surface on which they were deposited.

The transition are distinguished from the primitive in being aggregates of rounded particles, having little or no crystallization, and containing, or alternating with strata, which contain organic matter.

The oldest red sandstone, with all its accompanying strata, I should incline to put into the transition, as having many of the properties of that class, and occupying the same relative situation in the stratification of the globe. It is at a constant dip (although small) from the horizon; the cement is in greater quantities in proportion to the particles cemented than in any of the secondary aggregates, &c. &c.

The character of the secondary is a horizontal position, that perhaps does not admit of the same facility of examining the relative situation of its stratification. The compact limestone is, probably, with reason, considered as the lowest of the secondary formation, and always under the coal formation, but it appears to me that the secondary is deposited in basins alongside of one another, and that each basin has a different order of superposition, according to the nature of the agents employed in the deposition; that it is a partial, and by no means a general deposition. The secondary aggregates of sandstone and puddings have been evidently beds of sand or gravel, and of course, in that state would be called alluvial, but when cemented together by the infiltration of water, carrying along with it lime, iron, or any other body capable of agglutinating the particles together, become rocks, and may alternate in all proportions.

I am therefore inclined to think, that in geology the best mode for the greatest part of the secondary would be to give the relative position of the strata of each valley or basin; and I am rather of opinion that they would all differ from one another.

The French and English basin having chalk for the lowest stratum, which has occupied the geologists of both countries for these 10 or 15 years, is perhaps the best known; yet they do not know the relative position of the chalk and coals, because coals have not been found in the same basin with chalk: coals occupy basins filled with different kinds of rocks, and have no resemblance to the rocks found covering the chalk.