42 THE CANADIAN NATURALIST. [Vol. ix» 



cited ; but this is not necessary, since in mineral composition 

 typical diabase and doleryte are admitted to be identical. 



The facts as regards these two rocks, then, give no foundation 

 for the idea of such a transition epoch in rock-making at the 

 close of the Cretaceous period. And if not, it is bad for geology 

 to have such epithets as *' younger" and "older" treated with 

 so great distinction. 



Again: the difference between dioryte ("older") and ^^ro/jy- 

 lyte ("younger") is not in the chemical or mineral composition 

 of the rocks ; and hence, whatever difference there be is only in 

 texture and is, therefore, of little geological value. Agaiin, felsj/te 

 and tracfiyte are rocks of one and the same chemical and mineral 

 constitution. Ordinary felsyte consists of orthoclase, or ortho- 

 clase and olisroclase with sometimes disseminated hornblende or 

 quartz ; and the same is precisely the constitution of some kinds 

 of trachyte. They differ in aspect, and feel differently under the 

 fingers, and still some varieties of felsyte differ from ordinary 

 trachyte only in having the disseminated orthoclase crystals not 

 translucent, a difference of very small value mineralogically, and 

 not less so geologically. 



[^The rock of certain felsitic dykes ^in Canada and Vermont, 

 Paleozoic in age, is called trachyte by T. Sterry Hunt in the 

 Canada Geological Report, because of the essential identity with 

 that rock ; and Mr. G. W. Hawes, in his New Hampshire Report, 

 says (p. 187), of New Hampshire's " orthoclase-porphyry," 

 " Were it not that the feldspar is opaque othoclase, instead of 

 clear sanidin [that is, glassy orthoclase] one would immediately 

 think of trachyte on examining these rocks." Moreover, Messrs. 

 E. Reyer and Suess, eminent geologists of Vienna have shown 

 that trachyte occurs in the Euganean Hills of Cretaceous and 

 Jurassic age, as well as of Tertiary. Further, there are felsytes 

 among the "younger" rocks of the globe, that is, among the 

 products of volcanoes, where there is no trachyte ; and, on the 

 other hand, trachyte sometimes graduates indefinitely into fel- 

 syte. The facts show, consequently, that orthoclase rocks, or 

 orthoclase and oligoclase, have been erupted from Paleozoic 

 time onward, and that the distinctions found in some of the 

 latest kinds are superficial : a little rougher surface, more trans- 

 lucency in the feldspar, and some glass at times among the 

 crystalline grains ; but nothing that has any geological weight. 

 While then it may be well to retain the names of trachyte and 



