THE ADIRONDACK MOUNTAINS 7I 



lake, one north-flowing from the divide near the outlet of Forked 

 lake, and the other, south-flowing from the divide at Raquette 

 falls. These streams met to flow eastward into the Hudson river, as 

 Professor Lushing has suggested, either through the Sixniile-Fishing 

 Brook valle}- in the northeastern part of the Blue Mountain quad- 

 rangle, or through the Catlin Lake-Round Pond valley in the 

 southeastern part of the Long Lake quadrangle. In the writer's 

 opinion the best evidence favors the latter channel. Years ago an 

 attempt was actually made to cut a trench through this divide in 

 order to drain Long lake into the Hudson river. 



The famous Ausable chasm in Clinton county is a fine illustration 

 of a narrow gorge cut 200 feet deep into Potsdam sandstone by 

 the Ausable river since the Ice Age. The river was deflected from 

 its preglacial channel by a heavy blockade of glacial debris and 

 forced to erode this new channel. 



In the Lake Placid quadrangle there is a remarkable gorge known 

 as the Wilmington notch through which flows the West branch of 

 the Ausable river. The south wall of the gorge rises precipitously 

 600 to 800 feet, while the north wall is more than 1500 feet high 

 and very steep. In preglacial time there was a low divide instead 

 of the notch, with a south-flowing and a north-flowing stream from 

 it. The big glacial lake (see above) which occupied the valley south 

 and southeast of Lake Placid had its waters (known as upper 

 Lake Newman during an earlier stage) held up by the northward 

 retreating ice sheet whose front still filled the ^^'ilmington notch. 

 Further retreat of the ice permitted a lower stage of Lake Newman 

 to connect through the notch with waters in the Wilmington and 

 Keene vallevs. During this stage the connecting water flowed 

 southwestward through the notch and into a great lake in the 

 Saranac Lakes valley. With still further retreat of the ice. Lake 

 Newman disappeared; the standing water in the ^^'ilmington valley 

 ( Wilmington lake) discharged eastward ; and the drainage of that 

 portion of the basin of Lake Newman south and southeast of Lake 

 Placid, where much sediment had accumulated, was northeastward 

 as a stream flowing through the Wilmington notch. Thus was 

 inaugurated the flow, through the notch, of the present stream 

 which, aided by the broken up character of the rocks due to fault- 

 ing and excessive jointing, has cut a considerable gorge since the 

 Ice Age. 



Duration of the Ice Age and time since. Estimates of the dura- 

 tion of the Glacial epoch by the most able students of the subject 

 varv from 500.000 to 1,500,000 years. Such estimates are based 



