72 



WILLIAMS— DEEP KANSAN PONDINGS IN 



dated, like the cobble under the arrow in Fig. ii, which has been 

 cut on the right side until the fresh, white nucleus shows. These 

 facts force us to choose between a slowness of rock decay since 

 Kansan times that seems negligible, or a recency of that time ; as 



Fig. II. Crystallines from South Warren terrace-bar, showing mixture 

 of decayed and fresh pieces. Cobble under arrow has fresh (white) nucleus 

 exposed by rolling. 



the trenching of the Clarion and the deposit of these fresh rocks 

 occurred when the glacier had spent its maximum strength in sur- 

 mounting the Pennsylvania Highlands. Thereafter began its stag- 

 nation and wasting about Warren. 



Thompson Ponding. 



Elevation at beginning i,6io feet. The glacial margin had 

 spread over the entire Conewango Valley, and was over, or near 

 Thompson col. Grand Valley and Titusville were covered. The 

 water level about Warren rose over loo feet, and into it tumbled the 

 torrent at work excavating Big Bend Col which, at first, had a fall 

 of over 650 feet, and, when the Thoinpson level was formed, con- 

 tinued with 500 feet of head. The glacial energy was gone and 

 there was no more advance over the Highlands. 



