

XIII. ] GEOGNOSY OF THE APPALACHIANS. 271 



characters of those of Norway and of Anglesea, which, accord- 

 ing to Murchison and Giekie, are younger than the fossilifer- 

 ous limestones of the western coast (about the horizon of the 

 Levis formation of the Quebec group), which seem to pass 

 beneath them. Professor Nicol, on the contrary, maintains 

 that this apparent superposition is due to uplifts, and that 

 these crystalline schists are really older than the lowest Cam- 

 brians, which appear to the west of them as uncrystalline sedi- 

 ments resting on the Laurentian. He does not, however, 

 confound these crystalline schists of the Scottish Highlands 

 with the Laurentian, from which they differ mineralogically, 

 but regards them as a distinct series.* In the presence of the 

 differences of opinion which have been shown in this contro- 

 versy, we may be permitted to ask whether, in such a case, 

 stratigraphical evidence alone is to be relied upon. Repeated 

 examples have shown that the most skilful stratigraphists may 

 be misled in studying the structure of a disturbed region 

 where there are no organic remains to guide them, or where 

 unexpected faults and overslides may deceive even the most 

 sagacious. I am convinced that in the study of the crystalline 

 schists, the persistence of certain mineral characters must be 

 relied upon as a guide, and that the language used by Delesse, 

 in 1847, will be found susceptible of a wide application to 

 crystalline strata : " Rocks of the same age have most gener- 

 ally the same chemical and mineralogical composition, and, 

 reciprocally, rocks having the same chemical composition and 

 the same minerals, associated in the same manner, are of the 

 same age." t In this connection the testimony of Professor 

 James Hall is also to the point. Speaking of the crystalline 

 schists of the "White Mountain series, he says : 



" Every observing student of one or two years' experience in 

 the collection of minerals in the New England States knows 

 well that he may trace a mica-schist of peculiar but varying 

 character from Connecticut, through central Massachusetts, and 



* Quar. Jour. Geol. Soc. ; Murchison, XV. 353 ; Giekie, XVII. 171 ; Nicol, 

 XVII. 58, XVIII. 443. 

 t Bull. Soc. Geol. de Fr. (2), IV. 786. 



