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THE JOURNAL OF GEOLOGY.

with "igneous."[1] In the eastern United States Wadsworth was the first to declare for the volcanic origin of the felsites and tuffs in the Boston basin which, through the influence of Hunt's doctrine had, after Hitchcock's time, come to be explained as sediments. To Dr. Wadsworth also belongs the honor of having been the first geologist on this continent to insist on the original identity of these old lavas and pyroclastics with the recent volcanic rock of the Cordilleras.[2] There is little doubt that the finely preserved ancient volcanic material in the eastern crystalline belt and elsewhere will, when it is adequately studied, finally bring to this opinion most American geologists. If we as yet know little of the extent and distribution of our ancient volcanics, we are at least bound by no traditions to artificial and useless age distinctions, and may freely follow the lead of our English colleagues.

Criteria for the recognition of Ancient Volcanic Rocks.

It is a self-evident proposition that the identification of certain rocks as volcanic products is in no way dependent upon their present association with a recognizable crater or volcanic mountain. By volcanic rocks we understand igneous or pyroclastic material which has solidified or been deposited at, or very near the earth's surface. It is of little moment whether or not it was ever piled into conical mountains. That the rocks themselves bear witness to their origin and conditions of formation is sufficient. The successive effects of erosion on the easily removed volcanic mountains has been so often graphically described[3] that no further reference to the subject is here necessary. If the Eocene or Triassic volcanoes have so disappeared as to leave

  1. ↑ For instance, Ells in his "Geology of the Eastern Townships" (Can. Rept. for 1886, J.) speaks of pre-Cambrian rocks as "volcanic" and "plutonic," but enumerates only granite, diorite and serpentine.
  2. ↑ Bull. Mus. Comp. Zoöl., Vol. 5, 1879, p. 277 et seq., and Azoic System, ib., Vol. 7, 1884, p. 429.
  3. ↑ See, de la Beche: Geological Observer, pp. 526-537, 1851.M. Neumayr: Erdgeschichte, Vol. 1, pp. 202-204.W. M. Davis: "The Lost Volcanoes of Connecticut," Popular Science Monthly, Dec., 1891.
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