BUFFALO SOCIETY OF NATURAE SCIENCES 67 



which, during the Pleistocene, formed in the region about 

 Hudson Bay and spread thence radially over a vast tract from 

 the Arctic ocean to northern Pennsylvania and from the Atlantic 

 ocean to the Rocky mountains. The appearance of the northern 

 part of our continent at that time would have been identical 

 with that of Greenland to-day. This is still covered with an ice 

 sheet, the shrunken remainder of the great glacier which 

 uncounted thousands of years ago covered our county from view. 



The causes of the formation of this enormous sheet of ice are 

 unknown. To form such a glacier it would be necessary so to 

 change the climatic conditions of the northern part of North 

 America that the snow-fall of winter could persist through the 

 following summer. The cooling of an area of this size to a point 

 necessary for snow to persist through twelve months has been 

 ascribed to various causes. The slow swing of the earth's axis 

 in the precession of the equinoxes, or the elevation of the entire 

 area above the snow line would have been effective. 



The thickness and weight of the mass must have been 

 enormous. In Erie county we have no measure of its maximum 

 thickness. Gravel beaches at Springville were formed by a 

 lake of water penned into the Cattaraugus valley by the ice of 

 the retreating glacier. The lake marked by these beaches 

 drained southward through a channel at Machias at an elevation 

 of 1646 feet. The lowest point of the ice front therefore at this 

 stage of its retreat must have been more than 1646 feet above the 

 sea or approximately 1500 feet above the bottom of the depression 

 now occupied by L,ake Erie. Certain hills in Allegheny county 

 show no signs of glaciation above the 2200 foot contour. This 

 seems to mark the highest point of the ice sheet at its southern 

 limit. There seems little doubt that the site of Buffalo was 

 covered with ice to the depth of at least 1500 feet. 



The southward extension of the glacier was due, no doubt, 

 not so much to the existence here of a climate colder than our 

 present climate, as to the immense weight of the semi-plastic 

 mass. This spread outward from its center just as half-cold 

 coal-tar will spread on .a pavement. The enormous weight of 

 the ice at the north pressed outward the lower lying layers and 

 the whole mass thus spread imperceptibly but persistently. 



