XXXIV. Resume of the Geological History of 

 the Chautauqua Region 



1. Before the last geological period, the northern part of New York 

 had valleys and hills, plains and escarpments, very much as at the 

 present, though the details of topography were quite different. Among 

 the more important differences was the absence of the Great Lakes, 

 which occupy valleys that have been transformed to lakes largely by the 

 action of the glacier. 



2. Over this country the glacier ice slowly advanced until practically 

 the whole of New York was covered, and for a time this ice sheet 

 ground its way over the rocks, carrying fragments southward and 

 wearing down the valleys and the hills as it passed. All life was, of 

 course, exterminated from the region and the land was transformed 

 to a dreary icy plateau like that of central Greenland. 



3. At last, by some change in the condition of the climate, the ice 

 sheet began to melt away and to uncover the buried land. It seems to 

 have done this quite rapidly, though somewhat intermittently. That 

 is, it would stand for a time with its front edge along a certain line, 

 then quite rapidly melt away and transfer its front to a distance of a 

 dozen or so miles to the north, where it would again take a stand. 

 This is indicated by the moraines, which are irregular hills of glacial 

 deposits that were accumulated at the front of the ice. The glacier 

 was carrying a load of rock materials, and when these reached the front 

 they were dropped from the melting ice and therefore accumulated. 

 If the ice stood long enough a moraine was built along the margin; 

 if its stand was brief no moraine accumulations were made. One of 

 these moraines passes through Jamestown, another past the northern 

 end of Lakes Chautauqua, Bear, and Cassadaga, and in a general east and 

 west line back of the crest of the escarpment. Another line passes just 

 east of Silver Creek, one near Hamburg, and another through Crittenden. 



4. Beneath and in the ice was a load of rock fragments which were 

 moving southward. They were being ground over one another and over 

 the bed-rock, so that they were being reduced to clay by the scouring 

 action of the ice, which worked somewhat like a great sandpaper. 

 When the glacier disappeared, this material was left where it happened 

 to be, and so a soil was deposited which was composed of clay and 

 pebbles derived from various sources to the north. This till or bowlder 

 clay was dragged into many of the old valleys, either wholly or par- 

 tially filling them, so that the streams have often been obliged to cut 

 new channels in the shale. Sometimes these rock gorges end abruptly 



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