IO4 THE DAWN OF LIFE 



possible in addition to detrital volcanic material. But at that 

 time the crust itself, and even later stratified deposits would 

 often be kept for a considerable period at a high temperature. 

 Thus, not only rocks of igneous origin (including volcanic 

 ashes) would predominate in the lowest foundation stones, but 

 also secondary changes would occur more readily, and even 

 the sediments or precipitates might be greatly modified. As 

 time went on, true sediments would predominate over volcanic 

 materials, and these would be less and less affected by chemical 

 changes, and would more and more retain their original char- 

 acter. Thus we should expect that as we retraced the earth's 

 course through ' the corridor of time ' we should arrive at 

 rocks which, though crystalline in structure, were evidently in 

 great part sedimentary in origin, and should behind them find 

 rocks of more coarsely crystalline texture and more dubious 

 character, which, however, probably were in part of a like 

 origin, and should at last reach coarsely crystalline rocks, in 

 which, while occasional sediments would be possible, the 

 majority were originally igneous, though modified at a very 

 early period of their history. This corresponds with what we 

 find in nature, when we apply, cautiously and tentatively, the 

 principles of interpretation which guide us in stratigraphical 

 geology." 1 



This expresses very well the general result of the patient 

 stratigraphical and chemical labours of Logan and Sterry 

 Hunt, as applied to the vast areas of old crystalline stratified 

 rocks in Canada, and which I have had abundant opportunities 

 to verify on the ground. Under the undoubted Cambrian 

 beds of Canada lies the Huronian, a formation largely of 

 hardened sands, clays and gravels, now forming sandstones, 

 slates, and conglomerates, but with great beds of igneous or 

 volcanic rock, and hardened and altered ash beds. Under 



1 "The Foundation Stones of the Earth's Crust," 1888. The extract is 

 slightly condensed. 



