on geology and paleontology, 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 Europe to that of the north of Portugal. 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 sometimes 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.[1] It will be remarked that they run in a NW. and SE. direction, or almost transversely to the ranges of hills a, b, and c, which run NNE. and SSW. 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 six 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 present lines of drainage are determined. The greater number of the green chloritic fragments in
- ↑ This ground plan, and a further account of the Berkshire erratics, was given in an abstract of a lecture delivered by me to the Royal Institution of Great Britain, April 27, 1855, and published in their Proceedings.
