C H A PTE R IV. 



THE ALGONKIAN.' 



GEOLOGICAL DESCRIPTION. 



THE HINSDALE AREA.- 



Before my work had exteiuLid to tlie we«terri border of the region 

 covered by this study, my attention was called, in the winter of 1882, by 

 Prof J. D. Dana, to two interesting outcrops of undoubted Archean rocks 

 hi Hinsdale, a gneiss and a limestone containing chondrodite and a peculiar 

 peach-blossom-colored mica, determined by him to be probabh* rhodo- 

 chrome. Although these localities lie beyond the western border of the 

 river counties, the same rock extends into the southwest corner of 

 Middlefield, and Professor Dana's discovery was very acceptable to me as 

 furnishing a possible base to work from in the complex region under 

 examination. 



The two localities in question are at the first cutting west of the 

 railroad station in Hinsdale and at the first cutting south of tlie railroad 

 station in AVashington, and as they give a much fuller exhibition of the 

 series than the hmited portion of the same Avhich enters IMiddlefield, they 

 are made in the main tlie basis of the description following. 



The greater portion of the town of Hinsdale is occupied by an oval 

 anticline, elongated n(n-th and soutli and overthrown to the west. This 

 extends, much contracted, across Washington, and bending southeastward 

 and narrowing still more it enters Middlefield and runs along the south line 

 of tlie town to a point a mile beyond Becket station. The newer gneisses, 

 all down the east side of the anticline, dip normally eastward away from 

 the older, but here— that is, where the narrow band of Algonkian extends 

 east along the Westfield River— a sharp east-west wrinkle forms in the newer 

 gneiss, and the older gneiss buckles up through the newer. 



•Azoic (Lyell), Eozoic (Dawson), Archir-an, Dana. 



^This will be described in detail in a monograiih on the Archean of Berkshire County. 



19 



