426 H. L. FAIKCHII.D — GLACIAL GENESEE LAKES. 



feet more, as the Ontario basin was considerably lower than it is at 

 present. 



Proportionate to its length the h^ydrographic area is narroAv, being 

 only 40 miles wide at the broadest place, on the parallel of Silver lake. 

 Toward its northern terminus the valley narrows rapidly until for some 

 miles from the lake the river has no tributaries of consequence, and the 

 valley is merely the recent or })ostglacial ravine. 



The total area drained by the Genesee is estimated by Mr Bogart at 

 2,445 square miles. 



The form and dimensions of the vail e3^s of both the river and its tribu- 

 taries indicate, in the main, a mature drainage system. The old valleys, 

 where not drift-filled, are com])aratively open, broad and with gentle 

 grade. The dendritic form of the drainage in the middle and upper sec- 

 tions of the basin, wliich would be much emphasized 1)}'' indicating on the 

 map the smaller streams, is an evidence that glaciation has not there 

 greatly changed the ancient drainage. The important exceptions in the 

 lower part of the basin will be described below. 



The altitudes of the area are sufficiently indicated upon tlie map. The 

 figures given in connection with the names of towns and villages are the 

 heiglit of the rail in front of the railroad stations, referred to ocean level. 



DRIFT DEPOSITS. 



The amount of glacial drift still remaining in the valleys is very great, 

 probably surpassing in amount any similar deposits in western New 

 York. This is surprising when we consider the erosive power of the 

 present streams and the vast amount of drift that has certainly been 

 removed. In some localities tlie river valle}'' is sullicientl}^ o[)en, eitlier 

 by original absence of drift or l)y subsequent clearing, to i)ermit a view 

 of its original form, Ijut generally huge ridges or liills of drift obstruct the 

 view. In at least one instance the old river valley was so comi)letely 

 closed ))y the drift that the river has l)een diverted into a new channel, 

 and in the cases of side valleys and tributary streams this diversion of 

 drainage has been more frequent. 



In most sections the drift has ])een partially terraced or leveled by the 

 successive work of lakes and streams. The subsequent erosive atmos- 

 pheric agencies have, however, destroyed the water-planes in more or less 

 degree. 



The comi^osition of the drift deposits has not been determined to any 

 important extent. Casual observations suggest that much is ground mo- 

 rainal or till accumulation, but that probably the greater mass is water- 

 laid drift. 



