1 8 The American Geologist. January. 1901. 
This rock cannot be sharph' separated from the diabase 
just described, but passes into it gradually, many intermedi- 
ate types being found. The two rocks are thus apparently 
differentiation products of a single magma and any line of sep- 
aration between them could only be arbitrarily drawn. 
The rocks of the smaller division on the western side of 
the mountain consist, as has been said, of a succession of sedi- 
mentary and altered igneous rocks. The following horizontal 
section obtained by approximate measurements along the rail- 
way between Miletta and Eastman, will help to show the rela- 
tive position and extent of the two main divisions as well as 
of the subdivisions of the smaller part. The direction of the 
section is almost due west from Miletta. 
Sedimentary strata at contact i\.'it}i diabase near Miletta.. . 
' I. Diabase and gabbro-dioryte, main part of mountain, 7837 feet. 
(Graywacke, - - - 165 feet. 
,,) Serpentine, ophicalcvte etc.. - - 577 " 
^^- 1 Sandstone, .' . - 82 " 
(Serpentine, ophicalcyte etc., - - 1567 " 2391 feet. 
Sedimentary slates. 
The grevwacke is a greenish gray rock containing dis- 
cernible grains, some of which show vitreous lustre, while 
others do not. In the thin section the latter are found to be 
feldspar and the former quartz, while the greenish color is 
due to a micaceous-chloritic cement in which the grains are 
embedded. It is a clastic rock and a fairly representative 
specimen of a graywacke, belonging to the chloritic slates of 
Logan.* which is closely associated with the serpentines in 
many parts of the eastern townships, now recognized as Cam- 
brianf in age. It agrees in all essential respects with speci- 
mens from Potton and Shipton, which have been fully de- 
scribed by Dr. F. D. Adams.J 
The sandstone which occurs in this belt is of a light buff 
color and consists ni grains of feldspar and quartz of uniform 
size and often angular or subangular in form, which are 
cemented together by secondary silica, which, though not in 
large amount, occasionally shows ver)^ good examples of the 
*Geolosy of Canada, 1S63, p. 24-5. 
tMap to accompany Part J, Vol. VII, An. Rep. Geol. Survey of Canada, 
JOp. cit. pp. 19-21>. 
