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Sierra Club Bulletin. 



waves remodel the strand, obliterating much of the work 

 of the ice-thrust, but the shifted boulders remain where 

 the ice left them. The next winter's ice-sheet carries 

 them another stage in the same direction, and eventually 

 they reach the limit of its action. Thus all the boulders 

 which originally lay in the shallow water are finally as- 

 sembled along the shore, where they constitute the lake 

 rampart. 



Plate A shows a rampart on the west shore of Tenaya 

 Lake, not far from its outlet. On the land at the right 

 is a sprinkling of boulders, such as we may suppose to 

 have once existed on the lake-bed at the left, but none 

 now jut from the surface of the water. The larger 

 boulders of the rampart are three or four feet in diam- 

 eter, and in the distance there are two of still greater 

 size. But the largest may possibly occupy the positions 

 given them originally by the ancient glacier. Plate B 

 shows the margin of a lake on the plateau drained by 

 Rafferty Creek. The rampart here forms a broader ridge, 

 on which soil has gathered, so that it is covered by vege- 

 tation. Just here the lake has its outlet, which discharges 

 through openings between the boulders of the rampart. 

 In this view also may be noted the scattered boulders of 

 the adjacent plain, and the absence of boulders from the 

 shallow water of the lake. 



The theory is not a mere abstract deduction from 

 general principles, but finds support in a body of con- 

 crete facts. The cracking of lake ice from cold is a 

 familiar occurrence wherever winters are severe. As a 

 boy, in western New York, I skated on a landlocked bay 

 several miles long, and each winter its ice-sheet was 

 divided by cracks that ran from side to side. On a still, 

 cold night I have heard them form, the ice bursting with 

 a booming sound that slowly died away. I thought then 

 that a crack which started near me required a minute 

 or more to span the bay, but suspect now that its propa- 

 gation was much swifter than that of the sound-waves 

 on which my impression depended. Sometimes the cracks 



