W. E. Logan on the Rocks of Canada. 225 
upon them rest unconformably bluish slates, with intermingled 
bands of chert and limestone towards the bottom, and a thick and 
extensive overflow of greenstone trap at the top. Reposing on 
these are white sandstones, which pass by an alternation of colors 
into red sandstones and conglomerates, often with jasper pebbles, 
and these are repeated after the occurrence of an uncertain amount 
of reddish limestone of an argillaceous quality. The sandstones 
and conglomerates become interstratified with amygdaloidal trap 
layers, and an enormous amount of volcanic overflow divided into 
beds crowns the summit. The sandstones are often argillaceous, 
and display ripple-mark and crack casts on their surfaces, while 
the concentric curves of flow sometimes characterize those of the 
trap. Innumerable dykes cut up the sedimentary and volcanic 
beds, and both the dykes and the overflows are almost universally 
marked by a transverse columnar structure. ‘The thickness of 
the whole from the base of the blue slates cannot be less than 
12,000 feet, and the whole formation is intersected by copper 
lodes of different characters in different places, which run in direc- 
tions both with and transverse to the strike. 
tances from the nuclei; and then another set of greenstone dykes 
cuts through the intrusive granite, “isl 
causes had placed. Evidences of disturbances and dislocations 
| usions, those connected with 
Szcoxp Seats, Vol. XIV, No. 41.—Sept., 1852. 29 
