PUBLICATIONS. 229 
McConnel* reports a small area of Archean gneisses on the north- 
ern shore and neighboring islands of Lake Athabasca, on the islands 
of Lake Mammawi, and in the tilted deposits bordering Quatre Four- 
chés River. The gneisses include hornblendic, mieaceous, chloritic 
and epidotic varieties. In places they pass into a mica-schist or 
chlorite-schist. The gneisses strike from 10° to 20° west of north. 
Bell? describes the pre-Palzeozoic rocks of the north of Lake Huron 
as having been subjected in certain areas to vast denudation and decay 
before Paleozoic time. The evidence of this decay, most frequently 
found in granite, consists in hollows, pits, irregular ridges, and even 
small caverns, which are filled with Paleozoic limestone. These irregu- 
larities are regarded as having been formed at the bottom of the deep 
sea by solution. Had the erosion taken place on land there would be 
evidence of this in deeper decay in the substances of the rock and in 
the deposition of detrital deposits below the pure limestone, which in 
many cases rests directly upon the pre-Paleeozoic rocks. 
In the area between the foot of Lake Ontario and the head of 
Georgian Bay the contact of the Potsdam sandstone and Black River 
limestones with the underlying gneiss and quartzite is seen at many 
localities. These rocks are generally hard and fresh. The surface is 
irregular, and the whole has been buried beneath the horizontal 
Paleozoic rocks. 
Many of the long narrow valleys of the Archean region are due to 
the decay and removal of wide greenstone dikes or parallel dikes, 
with the belts of rock between them. The greenstone dikes are never 
found to traverse the overlying Silurian, and it is supposed that these 
valleys were mostly formed before the deposition of the Palaeozoic 
strata. It is thought that the larger part of this Archean area never 
received any of the Paleozoic rocks upon it, and that the surface of the 
Archean had been reduced to something like its present level and 
aspect before the Paleozoic deposits were deposited. As evidence of 
this are outliers of the Potsdam sandstone and Black river limestone 
filling similar narrow valleys. 
Comments. It may be suggested that the evidence given that the 
* Report on a Portion of the District of Athabasca, comprising the Country between 
Peace River and Athabasca River, North of Lesser Slave Lake, by R. G. MCCONNELL. 
Ann. Rep. Geol. Sur. of Canada for 1890-1, Vol. V, Part 1, D, pp. 5-62, 1893. 
? Pre-Palzeozoic Decay of Crystalline Rocks North of Lake Huron. Bull. Geol. 
Soc. Am., Vol. 5, pp. 357-366, pls. 15, 16, 1864. 
