214 SURFACE GEOLOGY. 



found at the same height over the Holyoke range, or upon Mt. Tom. 

 Allowing for the elevation of the river bed, this glacier must have ex- 

 ceeded 1500 feet in thickness in the Ammonoosuc valley, and probably 

 2500 feet at Windsor. From Prof. Dana's paper,"* it is obvious that the 

 ice continued a little west of south to New Haven, Conn., thus following 

 the depression of the valley to Long Island sound. The breadth of the 

 area showing striae conforming to the river's course is greater in Massa- 

 chusetts and Connecticut than in New Hampshire and Vermont, as might 

 be expected where the valley itself is broader. So far as can be conject- 

 ured, the heights are less in the more southern states ; and it is bounded 

 by the east of south course on both sides as sharply as further north. 



It would be repeating observations uselessly to print again the numer- 

 ous statements about the course of the striae along this valley given in 

 our table. That may be consulted to understand how fully the river 

 towns abound with groovings following the general course of the valley. 



Prof. Dana argues that the Connecticut valley ice moved towards the 

 sea at the same time that the great ice movement was in progress south- 

 easterly upon both sides, and explains it as the necessary result of a nat- 

 ural law. "It moves just as thick pitch poured over a sloping surface, 

 in which there are a few large groovings, would move, the mass follow- 

 ing the general surface, and the portions in the grooves nearly or quite 

 the course of the grooves. The thickness of the ice that followed the 

 course of the valley was at least 2,000 feet." Three considerations are 

 presented in favor of this view : — first, in Massachusetts and Connecticut 

 only the course with the valley has been observed ; second, if the glacier 

 were local, 2,000 or 3,000 feet thick, the southerly scratches ought to be 

 found further west than they now are ; third, there is more easting in 

 the course north of Massachusetts, as if produced by some part of the 

 general movement. I think it much better to believe the Connecticut 

 Valley movement was confined exactly to the limits where its evidences 

 are found, and to say that the south-east courses found here and there 

 within it are the relics of an earlier and grander glaciation. In fact, 

 when different parts of the same ledge, as in Hinsdale, show the courses 

 S. 10° E. and S. 60° E., no amount of argument can convince one that the 

 ice moved in both these directions at the same time. It is impossible. 



* Am. Jour. Science, \\\, vol. a, p. 233. 



