76 WILLIAMS— DEEP KANSAN PONDINGS IN 



through a marginal canyon at a low elevation, and westward into the 

 ponding of the old Clarion, as there is such a rapid westward slope 

 of the region that only within twenty miles below Franklin, in the 

 old Tionesta Valley, do its valley crests fall below 1,400 feet. Thus, 

 though the ponded water may have been backed up the old West 

 Sandy Valley against the Emlenton Col for thousands of years, with 

 increasing depth, it did not flow over it until the glacial lobe passing 

 down the western border of Pennsylvania had cut off the escape of 

 the ponding at lower levels. As the side movement of a lobe- 

 margin up hill is slow in comparison with the onward one of its 

 front down or along a slope, it is safe to take even smaller figures 

 for yearly progress than those suggested by Dr. Upham^° at Toronto 

 in 191 3, and take 15 feet per year as the average progress of a mar- 

 gin constantly scoured by a torrent, and 20 miles from the mouth 

 of old West Sandy Creek, as the position of the glacier when the 

 flow over Emlenton Col began. The margin must move 22 miles to 

 close that mouth, and with constant progress at the above speed 

 would require over 7,000 years before the Tionesta Ponding would 

 flow over Foster Col. As the trenching here is below present stream 

 level, and the stream flows over gravel, it is evident that another 

 long period intervened when the floods over Foster Col poured into 

 West Sandy Valley and over Emlenton Col, and before the former 

 col was fully trenched. We are now prepared to understand that, 

 long before this happened, the Emlenton Col and the portion of 

 West Sandy Valley between it and the Foster trench had been cut 

 down to their present levels. And yet there was a ponding of the 

 Tionesta against Emlenton Col after the Foster trench had been 

 fully sunk. There was thus a first and second Emlenton Ponding, 

 with the Foster Ponding as an episode between that reached far up 

 the old Tionesta. With the first we have no concern. 



Foster Ponding. 

 Elevation at beginning 1,500 feet. The trench walls on both 

 sides rise to this elevation. Reddish iceberg clay with scanty gravel 

 and cobbles is traced continuously to near this elevation on the hills 

 about Franklin and at Oil City. Just below this mark where the 

 country road from Franklin to Mays Mills dips down to Sandy 



