THE BEXCH IN NOKTHFIELD AND EKVING. (523 



quite liio-h, often up to or above the 300-foot contour, and tlie layer of till 

 above this is generally thin and not molded into drundins as on the west 

 side. Hence the bench sands are generally not of great thickness. They 

 represent mainly the deltas of Perchee and Northfield brooks. 



At the head of the deep recess formed by the soutlnvestward trend of 

 the valley's rim in the comer of Winchester, New Hampshire, is the ai)ex 

 of the delta of Perchee Brook (1 sh, PI. XXXV, C), at 392 feet above sea. 

 It consists of coarse deposits, with many rounded bowldei's of porphyritic 

 granite, even up to 2 or 3 feet in diameter. The brook runs at the foot 

 of the rocky ridge nearly to the State line, and all its delta is on its south 

 side. From its apex two roads run toward Northfield. The eastern runs 

 south at the foot of the cliffs and marks the eastern shore until, at L. 

 Lyman's, it turns into the plains toward Northfield street. The western 

 follows the brook until, just over the State line, it goes down from the 

 bench to the next terrace level (1 f) at 320 feet. 



Between these two roads runs a great island of till in the midst of the 

 delta plain. Just at the foot of this hill, on the side lacing the head of 

 the delta, is a triangular pond, 800 feet on a side, depressed 30 feet below 

 the level of the plain, its concave base embracing the island and its apex 

 pointing toward the head of the delta. From the other end of this island a 

 sandy esker ridge (k) extends southwest for a long distance, and just south 

 of ^Ir. D. L. Moody's main school building a cutting showed about 10 feet 

 of well-sorted sands; but I was informed that a little below coarse bowlder 

 beds occur. 



What is most remarkaljle in the deposits of this delta and its continua- 

 tion south in the high terrace is the great accumulation of fine sand. Soon 

 after leaving the hills the brook has cut deeply into these sands, and all the 

 brook sections in the neighborhood are in like material. Following the 

 brook down to where it descends sharply over the rocks to the liver plain, 

 these sands are seen to rest on clay at a height of 2!)0 feet above sea. Here 

 a line of springs marks the base of the sands, and immediately below aljan- 

 doned clay pits occur, as they do southward at various lower points in a 

 gorge cut by a tributary of this Ijrook and farther south by the roadside, 

 showing the clays to be continuous below the level of 290 feet. Following 

 the ten-ace southward, shallow depressions begin to appear in it, and oppo- 

 site the village street it has developed abundant well-formed kettle-holes 



