PHYSICAL AND CLIMATAL CONDITIONS. 129 



In March and April the marginal sheets break up into 

 floes, and drift up and down the bay, and the ice in the 

 bay is often reinforced by large fields from the gulf 

 without. These sheets of ice grind over the reefs and 

 impinge on the shores with great force, and, evidently, at 

 present, exert a great erosive and transporting power. 

 In the latter part of the Pleistocene period, when the 

 land stood at a lower level and the climate was, possibly, 

 colder, their action may have been still more powerful. 

 This action of floating ice is similar to that which has 

 been pointed out by Admiral Bay field in the river St. 

 Lawrence, and by the writer on the coast of Nova Scotia ; 

 but Mr. Chalmers believes that it has had a somewhat 

 exceptional power on the south side of the bay des 

 Chaleurs, which renders its influence there unusually 

 conspicuous and instructive. 



5. ICE IN TIDAL ESTUARIES. 



5. Still another form of ice-drift is that of ice-floes in 

 tidal estuaries, which is seen in, perhaps, its extreme 

 development in those of the bay of Fundy. In Acadian 

 geology I have noticed the removal of large boulders in 

 this way, and the Lower St. Lawrence may be regarded 

 as a tidal estuary ; but I have seen merely the effects, not 

 the actual operation, of the ice in winter and early spring, 

 and Hind has given so graphic and complete a picture of 

 the phenomena,* that I cannot do better than reproduce 

 it in his own words. The agency which he describes has, 

 not improbably, been concerned in the production of those 

 curious patches of sand and clay frequently seen in 

 boulder-clay and gravel beds, and whose origin is often 

 difficult to comprehend. 



* Canadian Monthly, Sept. 1875. 

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