346 On Eozoén Canadense. 
“The oldest known rocks of North America are those which 
Geological Survey of Canada, the e been shown to bea 
great series of strata, which, though profoundly altered, consist 
intervening mass of clay slates. This old gneiss, which is esti- 
ia we united thickness of these three great series may possl- 
bly far surpass that of all the succeeding rocks from the base 
the P 1 series to the present time. We are thus carried 
* 
1¢ same chemical and mechanic 
