EVIDENCES OF WATER-PLANES. 431 



less filled with drift of several kinds — moraine drift, kame drift and lake 

 sediments — and at once proceeded to open their channels. The reexca- 

 vation of the valleys has been wholly, and the leveling of the drift partly, 

 the work of the present streams. A renewal of the conditions of atmos- 

 pheric destruction in all its phases over all the area marks the last and 

 present stage. 



It will be noted as an important fact that there is a commingling, espe- 

 cially in the lower parts of the valleys, of the deposits formed during the 

 last three stages of the history. The terraces of the glacial and of the 

 morainal lakes and the detrital plains of the streams are intermingled 

 and confused. Sometimes it may not be possible to distinguish them. 



Phenomena of the glacial Lakes. 



evidences of water-planes. 



The phenomena proving the former existence of static water at high 

 levels in the Genesee valley are superabundant. To the observant eye 

 terraces and plateaus are scarcely ever entirely out of view. The phe- 

 nomena are of the various kinds characteristic of water margins, with the 

 addition of those peculiar to ice-dammed waters. They may be divided 

 into three classes : 



(a). Those marking the true level of the water, as beaches, lake-cliffs 

 and strictly shoreline features. For several reasons these features will be 

 weak. The waters were not very long stationary at any particular plane, 

 as they varied with the season and the down-cutting of the outlets, and 

 the expanse of water was not sufficient to permit of strong wave action. 

 The beach phenomena would give the most accurate data for altitudes 

 of the water surface, but they have not been observed. 



(h). Plateaus of superior level. Such are the deltas, of two kinds: (1) 

 Land-stream deltas, which will be recognized by their resting against the 

 valley walls and their relation to existing streams, which will have bi- 

 sected them ; (2) Glacial-stream deltas occur in the valley, removed from 

 the shore or isolated. By the removal of the ice-wall against which they 

 were headed the glacial streams which produced them were withdrawn 

 and such deltas are not bisected. They will usually be confused with 

 kame drift, to which, indeed, they are related. Even standing alone, as 

 butte-like plateaus, they resemble in their general form truncated or lev- 

 eled kames, which are of inferior levels. The allowance to be made for 

 the height of a true delta above the lake surface is a variable element. 



(c). Plateaus and terraces of inferior level. Here are included the 

 greater proportion of phenomena, as shoreline benchings, terraces of con- 



LI— Bull. Geol. Soc. Am., Vol. 7, 1895. 



