Note 290 — Chapter XL · THE MODERN VOLCANOES OF ICELAND AS ILLUSTRATIVE OF THE TERTIARY VOLCANIC HISTORY OF NORTH-WESTERN EUROPE

Captain C. E. Dutton, "Tertiary History of the Grand Cañon District," U.S. Geol. Survey (1882), p. 104.

[291] Captain C. E. Dutton, "Geology of the High Plateaux of Utah," U.S. Geol. Survey of the Rocky Mountain Region (1880), pp. 198, 200. See also pp. 232, 234, 276 of the same Monograph for additional examples.

[292] Tertiary History of the Grand Cañon, etc., p. 95.

[293] Nature, xxxi. (1884), p. 49.

[294] I may again refer to Hopkins's Researches in Physical Geology, where the conditions of the problem here discussed have been distinctly realized. Speaking of the ejection of lava from a number of fissures, he remarks that the imperfect fluidity of the melted material "would seem to require a number of points or lines of ejection as a necessary condition." "If there were only a single centre of eruption, a bed of such matter approximating to uniformity of thickness, could only be produced on a surface of a conical form." "Where no such tendency to this conical structure can be traced, it would probably be in vain to look for any single centre of eruption. On the supposition, too, of ejection through continued fissures, or from a number of points, that minor unevenness of surface which must probably have existed under all circumstances during the formation of the earth's crust, would not necessarily destroy the continuity of a comparatively thin extensive bed of the ejected matter, in the same degree in which it would inevitably produce that effect in the case of central ejection" (Cambridge Phil. Trans. vi. 1835, p. 71).