356 ICE-ACTION IN NORTH AMERICA. chap, xviii. 



on geology and palaeontology, I examined the glacial drift 

 and erratics of the county of Berkshire, Massachusetts, and 

 those of the adjoining parts of the State of New York, a 

 district about 130 miles inland from the Atlantic coast, and 

 situated due west of Boston, in lat. 42° 25' north. This 

 latitude corresponds in Eui'ope to that of the north of Por- 

 tugal. Here numerous detached fragments of rock are seen, 

 having a linear arrangement or being continuous in long 

 parallel trains, running nearly in straight lines over hill and 

 dale for distances of five, ten, and twenty miles, and some- 

 times greater distances. Seven of the more conspicuous of 

 these trains, from 1 to 7 inclusive, fig. 50, are laid down in 

 the accompanying map or ground-plan.* It will be re- 

 marked that they run in a N.W. and S.E. direction, or almost 

 transversely to the ranges of hills a, b, and c, which run 

 N.N.E. and S.S.W. The crests of these chains are about 800 

 feet in height above the intervening valleys. The blocks of 

 the northernmost train, No. 7, are of limestone, derived from 

 the calcareous chain b; those of the two trains next to the 

 south, Nos. 6 and 5, are composed exclusively in the first part 

 of their course of a green chloritic rock of great toughness, 

 but after they have passed the ridge b, a mixture of calcareous 

 blocks is observed. After traversing the valley for a distance 

 of ^x miles, these two trains pass through depressions or gaps 

 in the range c, as they had previously done in crossing the 

 range b, showing that the dispersion of the erratics bears some 

 relation to the actual inequalities of the surface, although the 

 course of the same blocks is perfectly independent of the 

 more leading features of the geography of the country, or 

 those by which the jiresent lines of drainage are determined. 

 The greater number of the green chloritic fragments in 



■-■■ This ground-plan, and a further livered hy me to the Royal Institu- 

 account of the Berkshire erratics, was tion of Great Britain, April 27, 1855, 

 given in an abstract of a lecture de- and published in their Proceedings. 



