16 GREEN MOUNTAINS IN MASSACHUSETTS. 



the general overfolding of Hoosac mountain and the Dalton-Windsor hills. 

 The limestone proper borders the whole western side of the area and ex- 

 tends well into the bay east of Cheshire. On the east side it also extends 

 visibly down from the north for some distance, but it then disappears under 

 a heavily drift-covered area. Going south from the limestone on this east 

 side, the first exposures we find belong to a continuous belt of the schists 

 connecting the Cheshire schist area with the tongue of schist infolded in 

 the Cambrian white gneiss farther east at the base of Hoosac mountain. 

 There is neither any trace of the limestone nor any room for it. 



On the south of the Cheshire schist area the Cambrian quartzite covers 

 the Dalton-Windsor hills, the topography of which is formed by the undu- 

 lations and intervening sharp folds of this hard mantle. The dip of the 

 undulating quartzite beds and the pitch of their sharp folds are both toward 

 the center of the Cheshire schist synclinorium. 



The Cheshire schist hills are separated from the higher Dalton-Windsor 

 quartzite hills by a narrow valley, which curves around the southern end of 

 the former with few exposures. But at one point quartzite and schist are 

 very near together, and it is evident that there is no room for the limestone 

 as such. In this valley there are large numbers of gneat angular blocks 

 and at least one ledge belonging to a transitional schist formation. I 

 repeat lure Dr. Wolff's description of this important rock: 



It resembles a micaceous white limestone tilled with little dark grains or imper- 

 fect crystals of feldspar. Under the miscroscope, in thin section, it is composed of a 

 mass of calcite grains, with here and there single grains of quartz, or an aggregate of 

 several grains, plates of muscovite and often of chlorite and biotite, and large por- 

 phyritic feldspar grains in single crystals or simple twins, very rarely showing poly- 

 synthetic twinning. These feldspars contain inclusions of mica, quartz, iron ore, 

 rutile, and calcite. and are in every way identical with the albites of the albitic 

 schists, although the exact species of plagioclase has not been determined. The 

 calcite seems to play the part which the quartz does in the schists: it sends tongues 

 into the feldspars or cuts them in two, and gives one the impression by its inclusions in 

 the feldspar, and its occurrence with the quartz and mica, that it is of contempora- 

 neous origin with the feldspar, mica, and quartz. 



This schist represents the landward transition of the Stockbridge lime- 

 stone into the Hoosac alhitic schist. Thus the Cheshire schist area is at its 



