HOOSAC MOUNTAIN. 97 



folded with the quartzite; second, the identity of the quartzite-conglom- 

 erate horizon underlying the limestone (that is, the Vermont quartzite) with 

 the fine grained white gneisses of the Dalton- Windsor area, and of these 

 with the white gneiss series of the central mass of Hoosac mountain; third, 

 the conformable contacts of the schist area in Hoosic valley with members 

 of the quartzite-white-gneiss series. 



HOOSIC VALLEY SCHIST. 



We have still to take up the relations of this large schist area to the 

 limestone. This rock is a typical schist, often gametifen ois, ci tming in places 

 close to the quartzite — at the "cove" within 250 yards. Near the quartzite 

 tongue on the western side of the "cove" we find the ground filled with 

 loose pieces of limestone and schist, with beautiful transitions between 

 the two rocks caused by the presence of the twinned plagioclases of 

 the schist in the limestone (see p. 64). It may be mentioned that the 

 same rocks occur in the beds of Mount Greylock. Only loose pieces of 

 this transitional material occur here, with one exception, but as they are 

 nearly on the line of contact of limestone and schist it can fairly be pre- 

 sumed that they are nearly in place and represent direct contact; one ledge 

 alone is exactly in place. The contacts of this schist with the quartzites of 

 the white gneiss series have been mentioned; in one case the schist under- 

 lies, in the other overlies. In the former case, near the large "canoe," we 

 know that the white gneiss series is inverted; in the other we know that it- 

 must be normal, and hence the position of the schist as overlying the 

 quartzite-gneiss is made clear. The Stockbridge limestone bounds this schist 

 on the west and northwest. At the southwest corner no contact is found, 

 although the two rocks come quite close together, the schist forming a hill, 

 the limestone lying in the valley at its base. The contact (concealed) runs 

 along to Cheshire Harbor, where limestone and schist are within 20 feet 

 horizontally. The two rocks have the same strike, north 35° east. The 

 dip of the limestone is 30° westerly; that of the schist is obscure, but 

 appears to be westerly. This seems, therefore, to be a, conformable juxta- 

 position, although actual contact is wanting. The line of contact runs 

 north for a mile, then doubles around the north ridge of the schist and runs 

 mon xxiii 7 



