MODIFIED DRIFT IN PISCATAQUA BASIN. I53 



place consist wholly of fine alluvium, and no coarse deposits were seen 

 farther south. Below Gonic these plains extend a mile wide to a distance 

 of two miles west from the Cochecho, and, excepting isolated hills, they 

 occupy the whole area between this and the Isinglass river. 



The height of these plains at Rochester is 226 feet, and at Gonic 200 

 feet above the sea, being at each place about 30 feet above the river. 

 Southward, the stream falls more rapidly than the plains, lying 75 feet 

 below them in the south part of Rochester. 



These deposits terminate near the mouth of Isinglass river; and the 

 next four miles of the Cochecho valley are destitute of modified drift, 

 which next occurs a fourth of a mile above the city of Dover. The river 

 has here cut through the ridge of a kame which extends from the kame- 

 like plain of Willand pond to that of Pine Hill cemetery. These were de- 

 posited by glacial streams, while the ice-sheet still remained unmelted on 

 both sides. After the ice had disappeared, Cochecho river brought down 

 the alluvial plain, composed of clay overlain by sand, on which the north 

 part of the city is built. The south part of this plain has been exca- 

 vated by the river, leaving the rest in the form of a terrace. Its height 

 is 70 feet above tide-water, which extends to its foot at Dover landing. 

 East of the city the river is again bordered by slopes of till or ledge. 



Fig. 37.-OBLIQUELY STRATI- Pig 38._Section in clay, Roch- 



FiED SAND, Rochester. ester. 



Scale, I inch=io feet. g^^j^^ ^ inch=io feet. 



Beds of clay are worked for brick-making a half mile south from the 

 Rochester depot, on the east side of the railroad, and a half mile farther 

 south on the west side of Cochecho river. At the former brick-yard the 

 clay is overlain by 5 to 8 feet of sand, which occurs principally in layers 

 separated by nearly level lines, as shown in Fig. 37, but obliquely lami- 

 nated with varying southward dip. About 15 feet of clay is exposed 

 here, the upper part being gray, and most of the lower part blue, defi- 

 nitely separated from each other. The section shown in Fig. 38 was 

 VOL. III. 20 



