10 THE JOURNAL OF GEOLOGY. 



with " igneous." ^ 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 vol- 

 canic rocks of the Cordilleras.^ 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 volcan- 

 ics, 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 pyro- 

 clastic 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 them- 

 selves 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^ that 

 no further reference to the subject is here necessary. If the 

 Eocene or Triassic volcanoes have so disappeared as to leave 



' 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. 



^BuU. Mus. Comp. Zool., 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. i, pp. 202-204, 1887. W. M. Davis: "The Lost Volcanoes of 

 Connecticut," Popular Science Monthly, Dec, 189 1. 



