22 THE POST-PLIOCENE. 



between tlie banks cast up by the Arctic currents of the present 

 American coast, and like those deep channels of the Arctic current 

 in the Atlantic recently explored by Dr Carpenter. Their arrange- 

 ment geographically, as well as their geological relations, correspond 

 with this view." 



" Another consideration with regard to the great lakes deserves 

 notice. Dr Hunt and Dr Newberry have collected many fticts to show 

 that the lake basins are connected with one another and with the sea 

 by deep channels now filled up with drift deposits. It is therefore 

 possible that much of the erosion of these basins may have occurred 

 before the advent of the glacial period, in the Pliocene age, when the 

 American continent was at a higher level than at present. Dr New- 

 berry has given in the Report of the Geology of Ohio a large collec- 

 tion of facts ascertained by boring or otherwise, which go far to show, 

 that were the old channels cleared of drift and the continent slightly 

 elevated, the great lakes would be drained into each other and into 

 the ocean by the valleys of the Hudson and the Mississippi without 

 any rock-cutting, and if the barrier of the Thousand Islands Avere then 

 somewhat higher, the St Lawrence valley might have been cut off 

 from the basin of the great lakes." 



" It would thus appear that in the Pliocene period the basin of the 

 lakes may have been a great plain with free drainage to the sea. 

 Instead of being afterwards occupied by a glacier, this plain and its 

 channels leading to the ocean were filled with clay at the beginning 

 of the Post-pliocene subsidence ; and at a later date the mud was 

 again swept out from those places where the Arctic current could most 

 powerfully act on it." 



In Chapter V. I have illustrated the power of coast ice in moving 

 boulders. Since this was written I have had the ojiportunity of 

 witnessing similar effects on a much grander scale in the estuary of 

 the River St Lawrence, and Professor Hind has described these 

 effects, as well as extensive polishing, on the coast of Labrador. He 

 says,* with reference to the great sheets of "pan ice:" — 



"'Pan' ice is derived from bay ice, floes, and coast ice, varying 

 from 5 to 10 or 12 feet in thickness, all of which are broken up 

 during spring storms. When the disruption of the ice sheet which 

 seals the fiords, the island zone, and the sea itself for many miles 

 outside, continuously, is effected in June, the resulting 'pans,' as the 

 fishermen term them, vary in size from a few square yards to many 

 acres in extent. The uniform and unbroken mass of ice in the winter 



* Paper read before the Natural History Society of Montreal, 1877, Canada 

 Naturalist, vol. viii. 



