HIGH-LEVEL DELTAS. 605 



level round the north of Bald Mountain and down the valley of Hartwells 

 Brook. 



One tinds few other traces of obstructed drainage marked b}- stratified 

 deposits of any extent across the high ground to the north line of the State. 



HIGH-LEVEL DELTAS. 



When the reservoir of Mill River broke through the dam at Williams- 

 burg, in 1874, the waters spread out fan-like after their first plunge in the 

 area, a few rods below the dam, and, rapidly losing momentum, they were 

 in effect suddenly overloaded and deposited immediately a portion of the 

 sand they were transporting, in an extended flat-topped layer 1 to 3 feet 

 thick, pushed forward in broad lobe-like projections and bordered down- 

 stream by a sharp terrace slope of 30°. 



All the streams which come down from the high grounds on the west 

 side of the basin in Westhampton, Northampton, Goshen, Williamsburg, 

 and Whately have here and there in their coui'se torrent deposits of a 

 size all out of proportion to their present dimensions, especially where the 

 streams, after running tlu'ough narrow channels, deboucli into broad, level 

 portions of their valleys. 



I am inclined to refer all these deposits to occasional violent floods when 

 the ice was melting in the upper part of ihe drainage area of the brooks 

 where they are found, and think they niay have been made much as were 

 the smaller terraces described above by the flooded Mill River in modem 

 times. At the same time, each one of them may have been formed while a 

 barrier of ice still filled the main valley and blocked up the mouths of these 

 east-west valleys, forming glacial lakes like those described above. 



There is one of these deltas on the upper portion of the Sawmill Brook, 

 on the road from West Farms to Westham})ton. It hangs in a remarkable 

 way over the broad valley, into which the stream passes here from between 

 the hills, its downstream slope being 40°, and its broad, flat surface 40 to 

 50 feet above the brook. It is brought out flush with the surface of the hills 

 on either side of the brook, as if it had been built up against a wall of ice 

 resting against these hills and filling- the valleys below. 



Two other deltas are found in the upper waters of the Mill River in 

 Grosheu, one at the first road crossing above the reservoir, where the brook 

 comes out of a naiTow gorge in granitic rocks. This is pushed out into the 



