606 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



valley, with broad, flat surface and steep downstream slope, and the stream 

 has now cut a deep channel in it to its base. The other occurs about a mile 

 below the reservoir on the same brook and east of Hubbard's ledge. This 

 is much larger than the one higher up, and its surface will include several 

 hundred acres. 



It is a very curious circumstance that every brook coming into either 

 of the transverse valleys of the Deerfield and Westfield rivers from the 

 north is flanked at its mouth by a distinct terrace, generally triangular from 

 the flaring of the valley, 65 to 100 feet above the sti-eam, and now divided 

 down its center by the deep cutting of the brook. At the villages of Charle- 

 mont, Zoar, Orange, and Huntington are fine examples. The explanation 

 that they were caused Ijy the ice lobe coming down the valley and being 

 thrown across the mouth of the side stream is uowdiere excluded by any- 

 thing I have seen, but it seemed to me possible that they mig-ht owe their 

 origin to sudden floods of overladen waters into the open valley in the 

 manner described above. 



The features at Charlemont admit of an easy interpretation upon this 

 supposition ; opposite the entrance of the tributary, and on the south side of 

 the Deei-field River, the high rocky bordei- of the river is set back in a large 

 semicircle, and the south half of this semicircle is still occupied by a great 

 body of sand and gravel, whose level surface slopes south as if in continua- 

 tion of the slope of the delta teiTace cm the other side of the main stream 

 and flanking the ti-ibutary. Indeed, if one could restore in"imaginatiou what 

 must, on this hypothesis, have been removed by the main stream and by 

 the tributary itself, the great body of sand would form an alluvial fan extend- 

 ing right across the valley of the Deerfield into the great cirque described 

 above, the southern portion of which fan has since been separated from the 

 rest b)'' the erosion of the Deerfield. However, a southward-sloping terrace 

 on the south side of the Deei-field would not be an impossibility, and the 

 rock of the region is so monotonous that it gives no clew to the source of the 

 sand. These terraces were called delta terraces by President Hitchcock.' 



In order not to multiply colors, I have colored these delta teiTaces with 

 the same shade as that which would be applied to them if they were "glacial 

 lakes" — that is, sands deposited by the obstructed drainage during the retreat 

 of the ice. 



' Surface Geology, p. 32. 



