I08 SURFACE GEOLOGY. 



the sand being deposited in autumn and spring. The line of downfall, 

 A-A, apj^ears to show where these materials at first rested against a wall 

 of ice. When this melted, the strata suddenly fell as seen at these 

 points. 



In Hancock, a mile and a half farther west, the first excavation for this 

 railroad after crossing the highway shows sand and fine gravel under- 

 lying till upon both sides of the cut. (Fig. 26.) This is on the south 

 slope of a hill, at a height for the bottom of the cut of 28 feet above the 

 river. The surface all around is composed of till and covered with 

 boulders. The separation between the modified drift and till is not a 

 definite line ; but there is a gradual transition, occupying one or two 

 feet, and the till has thin streaks of sand. No boulders were seen in 

 the underlying deposit. 



Fig. 26. — Section of Modified Drift under Till, 



Hancock. 



Length of Section, 300 feet; height, 15 feet. 



1. The unmodified drift, or till, contains boulders of all sizes up to 8 or 10 feet; its 

 thickness is from 6 to 10 feet. 



2. The modified drift is stratified in layers of varying thickness ; sometimes con- 

 torted, but mainly horizontal ; consisting of sand (in strata from 2 to 5 feet thick) and 

 fine gravel (with the largest pebbles 3 inches in diameter) ; thickness exposed, from 5 

 to 7 feet, also extending below the excavation. 



The lack of alluvial deposits in the Contoocook valley is made up 

 where we might least expect it, two miles farther east, at a height of 

 nearly 200 feet above the river, and not in the pathway of any large 

 stream. Following the stage road from Bennington to Greenfield, 

 numerous kames were seen north-east from Pollard pond, principally 

 forming north-west to south-cast ridges, and composed of coarse gravel. 

 The road next enters on a nearly level plain of sand and gravel, which 

 extends about two miles to the south, being from one half mile to one 

 mile wide. Its height is from 850 to 870 feet above the sea. Hog- 

 back and Bridge ponds lie in depressions of this plain, with steeply 

 sloping shores from 25 to 30 feet high. Pollard pond lies about 50 feet 

 below the plain, of which with its outlet it forms the western boundary. 



