600 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



through a curious narrow canyon, in the bottom of wliich Wright's brook 

 now rises from a large spring. Down the course of this brook the waters 

 passed to join those of the WiUiamsburg Lake. 



THE BEAR RIVER LAKE. 



The fulhiess with which all the evidence concerning the formation of 

 the deposits in this basin can be traced leaves little to be desired. The 

 basin is a broad one, extending, with its greatest dimension east and west, 

 across the line between Ashfield and Conway (middle of PI. XXXV, A). 

 It is surrounded on all sides by high ground, except a narrow passage at 

 the nortlieast corner, and sends three great lobes northward among the hills. 

 In its southern part it is filled to a great height by an enormous volume of 

 coarse sand, especially in the area around the cemetery at School No. 2. 

 The height to which these sands were brought up was determined by the 

 height of the col at the s(5uthwest portion of the basin by which the waters 

 escaped into the Ashfield Lake along the road which runs south to Ashfield 

 Plains. These sands were brought in while tlie ice was retreating from the 

 valley and still filled its northern parts, as in all the northern portions of the 

 basin the sands occupy a lower level, and it is plain that they were never 

 heaped up to the height of the south-side sands and then eroded. It is there- 

 fore probable that the north side of the basin was still filled with ice when 

 the latter were brought in, as they must have come from the north. 



When the ice had completely left this basin it marked its next halting 

 place with beautiful clearness. The water maintained its former level after 

 this retreat, this being conditioned by the col in the southwest corner. It 

 carved a broad bench in the till around the north border of the lake and 

 brought in great bodies of sand over its bottom, but not enough to fill it. 

 If these sands are followed to the northeast corner of the basin, they are 

 found to extend a distance along a narrow rock-bottomed valley, scarcely 

 covering the rocky floor. The rock bottom of the valley then sinks rap- 

 idly, while the sands widen somewhat and continue at the old level, thus 

 filling the deepened valley with beds of very great thickness. At a cer- 

 tain point in this ^'alley they end abrujitly (b"), and one goes down by 

 a great lobed scarp to the deep valley bottom, and for 100 rods down- 

 stream (northwardly) the steep valley sides are strewn with glacial bowlders 

 to the water's edge. These sands ai-e grooved in the middle by the Bear 



