HOGS AC MOINTAIN. 73 



Finally the limestone borders this last area on the west. The relations 

 of these rocks — granitoid gneiss, white gneiss, and metamorphic conglom- 

 erate — are best shown at the extreme northern end of the area of the first 

 rock (see Profile ix, PL v) on the crest of Hoosac mountain. The granitoid 

 gneiss is here of tin- typical variety, with bright blue quartz and a structure 

 well marked in the mass. This dips about 10° to 15° a little cast of north. 

 In a little north and south cleft, just south of a small swamp, we find this 

 rock in contact with the overlying conglomerate gneiss. Fig. 27 shows 

 this. The series dips 20° in a direction north 25° east. The lower part 



Fig. 27.— Contact of irranitoid gneiss (Stamford gneiss) ami metamorphie conglomerate (Vermont formation). Top of 

 Hoosac mountain. South ol Spruce hill. 



The contact runs from the left hand lower corner to the right hand upper corner. This conglomerate is also shown 

 in Fig. la. Notice that the lines of structure of the gneiss -follow conformably those of the conglomerate. 



of the exposure is formed of tvpical granitoid gneiss. Upon this the 

 lower beds of the white gneiss-conglomerate rest conformably. In the latter 

 rock it is apparent at once that crushing has largely affected the form of the 

 pebbles. To this cause their flattened character and truncation by oblique 

 planes of mica is undoubtedly due, and yet they are in large part pebbles. 

 Not only their general shape, but the lithological distinctness shows this. 

 They are composed either of massive white quartz, or blue quartz, or smoky 

 quartz, or in some cases of a white granulite, or lastly of a line grained white 



