ESKAR EXCAVATION IN NOVA SCOTIA. PREST. 37 



Beds No. 8, 9 and 10 were deposited under a variable 



but gradually lessening turbulence of waterflow. First, gravel 



and coarse sand, then fine sand. Then came a 



Variable rather sudden change to extremely quiet condi- 



condttio7is tions when a very finely laminated clay was laid 



down. This clay could be deposited only when 



a former outlet was dammed by debris and the resultant 



current capable of moving only the very finest material. 



This tranquil condition ended in a period of slight erosion. 



On the fine clay was laid the fine sands of bed No. 11, 



followed again by erosion which cut deeply into the southern 



side of the eskar. The cause of this erosion is 



Erosion referred to later. 



Then succeeded alternating conditions, during 

 which were deposited the gravel and sands of 

 bed No. 12 and the coarser material of bed No. 13. 

 Thence, to the top of the eskar, the deposits showed the 

 results of alternating rapid and moderate currents. All these 

 upper beds showed the confusing postglacial effects of frost 

 and the growth of vegetation. 



Now let us summarize the possible history of this deposit. 



At the beginning we have a provincial if not a continental 



glacier. All large glaciers show crevasses, and 



Summary our Nova Scotian glacier could hardly have been 



of history an exception. The cause of the formation of ice 



crevasses is evidently a tension or strain which 



reaches its breaking point where the slope of descent changes 



to one more or less steep. This is the case both in Greenland 



and on the Antarctic continent. It must have been so at 



Middlefield, where we have to the south a gentle tho fairly 



even slope and to the north a flat lake region. And yet this 



eskar does not lie exactly on the edge of the lake region, but 



a short distance to the south. At the edge of the lake region 



we have a few short ridges, evidently the beginning of another 



system of crevasses, which in time might have become the 



seat of a prominent eskar. 



We have here support for the belief that crevasses, after 



their successive formation across a continental ice sheet, 



were carried forward in the general advance 



The until climatic changes called a halt. The surface 



theory water, pouring into the debris gathered each 



summer, sufficed to keep the crevice open until 



