352 THE ICE AGE IN NORTH AMERICA. 



waters of the Piscataqua River. Thus there was, along a 

 certain margin of the ice, a backward drainage of twenty 

 miles or more, which offers a ready explanation for this 

 seeming anomaly in the relation of the kame to the general 

 slope of the valley down which the ice had moved. 



Several other instances, equally marked, described by 

 Professor Lewis,* exist in the eastern counties of Pennsyl- 

 vania. In these cases a great amount of glacial debris had 

 been deposited upon the ice, a little back from its front, on 

 the west side of the Delaware River, both above and below 

 the Water-Gap. South of the Water-Gap these deposits are 

 several hundred feet higher than the Delaware River, and 

 lie between it and Kittatinny Mountain. When the Dela- 

 ware had opened its own channel back to the present site of 

 Portland, just below the Water-Gap, a line of backward 

 drainage was established from the higher land on the south- 

 west toward the northeast. This line is now marked for a 

 number of miles by a very well-developed system of kames. 



A similar line of kames descends the valley of Jacobus 

 Creek along the line of drainage to the Delaware River, 

 sloping backward from the glacial margin near Johnson- 

 ville toward Stroudsburg. Down this backward slope, for 

 a distance of five miles or more, the kames are very con- 

 spicuous. 



The gravel-ridges occurring in the southern or upper end 

 of the numerous transverse valleys containing the Finger 

 Lakes of central New York seem to be similar instances of 

 kames formed by backward drainage. The course of events 

 there seems to have been as follows : After the ice melted 

 back to the water-shed between the Mohawk and the Sus- 

 quehanna River, a large amount of water-worn material 

 accumulated upon and about the margin before the great 

 line of drainage through the Hudson and Mohawk Rivers 

 opened. When, finally, the streams of this region were re- 



* " Marginal Kames," in " Proceedings of the Society of Natural Sciences," 

 Philadelphia, June 2, 1885, pp. 167-173. 



