42 



SURFACE GEOLOGY. 



which they appear to have been carried up by the prevaihng north-west 

 winds. Southward they are found in many places on the east side of this 

 valley, but none were seen in Vermont. 



Deltas. A large amount of modified drift occurs on Blow-me-down 

 brook. Three miles from its highest source, where the road crosses 



Fig. II. — Sand Dune, near the South Line of Lebanon. 



Croydon mountain, it has formed the plain of Cornish Flat, 855 feet above 

 the sea, and six miles lower that of Plainfield village, 520 feet above the 

 sea, with an older deposit 30 feet higher, at the north end of the village. 

 Two miles farther down, where this stream opens into the broad valley, it 

 has formed a delta of irregular slope from 512 to 420 feet. These trib- 

 utary deposits often throw light on the history of the modified drift of the 

 main river. We have seen that the deltas north of the continuous kame, 

 as of Wait's river at Bradford, and Jacob's brook at Orford, were deposited 

 before the completion of the original flood-plain of the Connecticut ; but 

 the deltas of Quechec river and Lull's brook appear to have been brought 

 down at about the same time with this upper terrace, which is notably 

 increased in height by them for a considerable distance; while the long 

 sloping delta of Blow-me-down brook, covering a square mile and descend- 

 ing to nearly 100 feet below the normal highest plain, seems to be of 

 a date subsequent to its formation and partial removal by the river. A 

 conspicuous dune at the east side of this delta, derived from it and from 

 the original high plain, is 610 feet above the sea, or 100 feet higher than 

 the deposits from which it was blown. 



