Carney — Possible Overflow Channel of Ponded Waters. 217 



Art. XXIII. — A Possible Overflow Channel of Ponded 

 Waters Antedating the Recession of Wisconsin Ice', by 

 Frank Carney. 



Introduction. 



When the ice-eap extended into Pennsylvania south of the 

 " Lake region " in central ]STew York, the Susquehanna through 

 its tributaries carried off the augmented drainage. Following 

 this maximum reach of the ice came a period of decline marked 

 by successive retreats and halts. In withdrawing from the 

 Alleghany plateau area the front of the ice became grossly 

 serrate, the pattern of the longitudinal valleys of the outer 

 slope of the plateau. Each valley held a lake which grew 

 deeper and broader as the ice-barrier receded. The Susque- 

 hanna was still the ultimate drainage-line of ice-front waters. 

 Each lake retained an outlet southward till the ice uncovered 

 some new point northward lower than the altitude of this over- 

 flow channel ; then the lake coalesced with the water-body in a 

 neighboring valley, still reaching the Susquehanna, but by a 

 less direct route. In time the glacier revealed altitudes so low 

 that the impounded waters were no longer carried to the 

 Atlantic by the former course, but went first to the west, over- 

 flowing ultimately by the Chicago outlet, and later eastward 

 via the Mohawk. 



It is apparent that when the ice had retreated along a partic- 

 ular divide between two adjacent north-sloping valleys far 

 enough to allow the water-body having the higher level to flow 

 into the other, the line of flowage was at first either a channel 

 with ice for one wall, in which position the overflow stream 

 might intrench itself provided the ice kept a constant front ; 

 or a sag in the divide, a location that the overflow would main- 

 tain until the ice had withdrawn from a level lower than the 

 bed of the stream. Successive stages of coalescing ice-front 

 lakes would thus develop channels transverse to the intervalley 

 divides. 



local Ice- Front Lakes. 



The two unreported channels that occasion this paper mark 

 stages of an ice-front lake or lakes in Keuka valley ; an 

 impounded lake occupying Seneca valley constituted the local 

 base-level of these channels. 



Resume* — The first ponded body (HammondsiJort Lake )+ 



* See this Journal, vol. vii, 1899. Professor H. L. Fairchild's map, Plate 

 vi, in his paper, "Glacial Lakes Newberry, Warren, and Dana in Central 

 New York," pp. 249-263, will aid in following this brief description. 



For a bibliography on the history of the high level ice-front lakes see foot- 

 note to p. 325, vol. xxiii, 1907, of the Journal. 



f H. L. Fairchild, loc. cit., p. 253. 



Am. Jour. Sci.— Fourth Series, Vol. XXV, No 1 : 147.— March, 1908. 

 15 



