432 H. L. FAIRCHILD — GLACIAL GENESEE LAKES. 



struction (wave-built), terraces of erosion (wave-cut) and truncated hills 

 of moraine or kame drift. The allowance to be made for the higher alti- 

 tude of the water surface is here assumed in general at from 10 to 20 

 feet, or less for coarse materials. 



In the very rapid and cursory examination of this large region it has 

 been impossible to discriminate as to the exact nature of the plateaus 

 and terraces measured for determination of water-levels. The one essen- 

 tial fact was the certainty of their being phenomena of water-planes. For 

 the purpose of correlation with the several lake outlets only the highest 

 terraces of each section are relied upon, which are far above any possible 

 stream action or even the level of moral nal lakes, and too far reaching 

 to be the result of mere lakelets upon the side of a glacier lolie. 



As each stage of these glacial waters covered only a limited section' 

 north and north, and had its own independent levels and, geologically 

 speaking, was of brief duration, the distortion of water-planes due to dif- 

 ferential northward uplift is probably of small amount. 



DRAINAGE OUTLETS. 



Upon the map (plate 19) the important channels across the divides are 

 indicated by lines and the altitude above tide b}^ figures, placed trans- 

 verse to the line of ^vater-parting. Those at the three cols in which the 

 river heads were doubtless contemporary outlets of the primary lakes. 

 One of these, between Rose lake and Oswayo, is believed to have sub- 

 sequently taken the water from the other two. The channel northwest 

 of Genesee village is cut down to the grade of the valley. Tliis, like the 

 preceding Oswayo outlet and the subsequent Cuba outlet, carried the 

 Genesee waters to the Allegany river and the Mississipi)i. Tlie third 

 great outlet with two subordinate phases was upon the eastern divide 

 above Hornellsville, leading to the 8us(|uehanna waters. The next outlet 

 was over the western divide into the great lake W^arren. These outlets 

 will be briefly described below in connection with their respective lakes. 



THEORETICAL STATEMENT. 



A general theoretical statement of the succession of glacial lakes will 

 clear the wa}- for the detailed description of those lakes, ^\'e have a 

 comparatively narrow valley, with numerous side tri})utaries, sloi)ing 

 northward or toward the retreating ice-front. By the northward shifting 

 of the ice-dam, the impounded waters fell from time to time to the level 

 of each successively lower outlet over the divide. In any section of the 

 valley the highest water-plane should correspond to the lowest outlet 

 uncovered. In want of knowledge it is assumed that the ice-front was 



