GEOGNOSY OF THE APPALACHIANS. ' 479 
ern coast (about the horizon of the Levis formation) which seem 
to pass beneath them. Professor Nicol, on the contrary, maintains 
that this apparent super-position is due to uplifts, and that these 
crystalline schists are really older than either Cambrian or Silurian, 
both of which appear to the west of them as a stalline sedi- 
ments, resting on the Laurentian. He doe t, however, con- 
found these crystalline schists of the Sabttink 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 controversy, 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 ap- 
plication to crystalline strata. ‘Rocks of the same age have 
most generally 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 
ag a” f ` 
In this connection the testimony of Professor James Hall is to 
the point. FEE of the crystalline schists of the White Moun- 
tain series, he sa 
“ Every eA student of one or two years experience in the 
Soran of minerals in the New England States, knows well that 
trace a mica-schist of peculiar but varying character from 
R through central Massachusetts, and thence into Ver- 
mont and New Hampshire, by the présence of staurolite and some 
other associated minerals, which mark with the same unerring cer- 
tainty the geological relations of the rock as the presence of Pen- 
tamerus oblongus, P. galeatus, Spirifer Niagarensis, or S. macro- 
pleura, and their respectively associated fossils do the relations of 
the several rocks in which these occur.” į 
*Quar. Jour. Geol. Soc.; Murchison, XV, 353; Giekie, XVII, 171; Nicol, XVII, 58, 
ah 
Bull. Soc. Geol. de Fr. (2), IV, 786. 
Arla gs p New York, Vol. III, Introduction, page 93. 
