358 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
strong resemblance to a quartz-diorite. As these rocks make fairly good 
thin sections, a number were made and in every case the section showed 
that the rock was largely made up of quartz fragments. A thin section 
of a specimen from the long point running out into Lake Wendigokan on 
the west side of HF21, contains a few fragments of hematite, and a hand 
specimen from some similar arkose on Lake Wawang, much farther east, 
shows some small fragments of the same mineral. Where the latter 
specimen was taken the arkose is rather coarse and is closely associated 
with some of the conglomerate very richin jasper pebbles. An interesting 
specimen from near the middle of the south side of location HF 19 on 
Lake Wendigokan, very much resembles a conglomerate on account of 
some concretionary structures which in the hand specimen look like 
pebbles. Under the microscope there may be seen small mosaics of quartz 
among the angular fragments, also badly decomposed plagioclase, some 
zoisite, orthoclase and chlorite. In some of the specimens, part of the 
quartz fragments are fairly well rounded, showing water action. It is 
a little hard to account for so much quartz in these rocks unless they ori- 
ginated from granites and were carried down from the north by streams, 
but the fact that the quartz is so much more resistant than the other 
minerals and would, therefore, remain while the others would be decom- 
posed and carried away, would help to explain this condition. Much of 
the sand so plentiful along the streams and lakes in this region probably 
originated from the decay of these rocks. 
THE KEWEENAWAN;—Basic ERUPTIVE. 
The only outcrop of the post-Keewatin basic eruptive found in the 
region is that west of Lake Wendigokan and crossing the trail between 
the Sturgeon River and Lake Corrigan. This rock is responsible for the 
long rapids on the Sturgeon, and it is quite probable that the large outcrop 
extending some distance along the east shore of Lake Nipigon is a continua- 
tion of the same mass almost directly westward from where it crosses the 
Sturgeon. It has proved difficult to fix definitely the age of this rock, 
because it represents the only system found in the region between the 
Lower Huronian and Pleistocene, but its strong resemblance to other 
Keweenawan rocks of the Nipigon region are very much in favour of placing 
it in the Keweenawan system, and though there is plenty of room for 
difference of opinion on the classification, in my opinion that is the system 
to which it belongs. } 
This mass of eruptive has some appearance of being an intrusive 
sheet with its broad flat areas on top and, though the contact is usually 
