30 H. L. J<'AlJirilIJ>l) — (iLACIAI. WATKIIS IN KINOKJI l.AKKS KKGION 



chiefly a plain description of tlie more important features of these ancient 

 lakes. The matter is of livel}^ interest to i)erha})s only a fcAv persons, 

 but the details are necessar}^ to the uiore general study of the Pleisto- 

 cene. No economic or practical result from the knowledge is foreseen, 

 but as pure science the study of these waterless lakes, waveless shores, 

 and streamless channels has a fascination and romance. Its immediate 

 results are of some value in helping to determine the conformation of 

 the glacier front during its recession, and the deformation of the land 

 surface since the shoreline features were produced. 



A glacial lake is defined as a body of static water existing by virtue 

 of a barrier of glacial ice. It will be evident upon slight reflection that 

 such impounded waters can exist (1) whei'e a glacier blocks a stream 

 channel, or ("2) where the general land surface inclines toward the gla- 

 cier foot. Lakes of the first class have been described in Pennsylvania 

 by I. C. White, in the Monongahela valley,'^ and by E. H. Williams, in 

 the Lehigh valley f and the Susquehanna valley. X 



All the lakes described in this paper belong to the second class. They 

 were formed in the southern part of the Ontario basin, where the land 

 slopes northward from a plateau of 2,000 feet elevation down to lake 

 Ontario, 246 feet. The high plateau was deeply gashed by the pregla- 

 cial stream erosion, and in these trenches along the northern border of 

 the plateau lie the present "Finger" lakes. The topography was pecu- 

 liarly favorable to the production against the bold ice-front of a series 

 of distinct valley lakes, in man}^ respects unequaled elsewhere. 



The preglacial drainage of the region was northward and the heads 

 of the rivers were probably much farther south than those of the present 

 streams, perhaps even in Pennsylvania, like the present Genesee river. 

 Theoreticall}^ the oncoming ice-sheet met and blockaded the preglacial 

 rivers and impounded their waters in the north-sloping valle3"s. The 

 phenomena of those early glacial lakes caused b}^ the advance of the 

 glacier have been so destroyed or obscured b}^ the overriding of the ice 

 and by its del)ris that no certain evidences have 3^ et been distinguished. 

 We have therefore for our objective study only the lakes, far later in 

 time, produced in the same valleys b^^ the damming action of the ice- 

 front in its retreat back to the north. 



According to size and im})ortance, the glacial waters which we have to 

 consider ma}' be divided into three groups : (1) Primitive and smaller 



♦Origin of the High Terrace Deposits of the Monongahela River. Am. Geologist, vol. xix, p. 368, 

 Dec, 189G. 



t Extramorainic Drift between the Delaware and the Schuylkill. Bulletin of this So<-iety, vol. .5, 

 p. 286, March, "189-1. 



J Notes on the Southern Ice Limits in E;istern Pennsylvania. Am. .lour. Soi., vul. xlix, p. 18.3, 

 March, 1895. 



