74 GREEN MOUNTAINS IN MASSACHUSETTS. 



gneiss containing blue quartz and biotite. In one large pebble the gneissoid 

 structure in it is quite oblique. It is easy to see that this conformity of con- 

 tact in these two rocks, both of which have so much secondary structure 

 developed in connection with crushing, may be due to the crushing itself. 

 From this contact northward the crest of Hoosac mountain makes a sharp 

 rise in a series of bluffs facing south, the top of each bluff sloping gently 

 to the north. Profiles a and B, PI. XI, show this feature well. In PL XI, b, 

 we are looking west; in the hollow at the extreme left is the contact 

 spoken of, and the white gneiss-conglomerate extends to a point shown 

 about the middle of the picture, and is then succeeded by the albite-schist. 

 The gentle northerly dip of the whole series can easily be seen by the 

 slope of all the steps of the crest to the north (right). See also PL v, 

 Profile ix. Starting from the granitoid gneiss at the base we find a 

 thickness of 600 to TOO feet of this white gneiss conglomerate with a very 

 steady northerly dip of 15° to 20°. At the base the rock is quite coarse, as 

 previously described. As we ascend in the series it becomes gradually finer 

 grained. The granulite-gneiss pebbles become smaller and smaller and are 

 more frequently crossed bv the mica of the groundmass; the quartz pebbles, 

 and especially those of blue quartz, preserve their rounded character. Fig. 

 20 (from a large cliff of this medium grained rock) shows this character 

 finely; the large pebbles are mainly of blue quartz. As we go higher up 

 the rock becomes more and more even grained until we get a finely banded 

 muscovite-biotite-gneiss. In many places the conglomerate is finely crum- 

 pled or fluted, the axis of these foldings gently inclined, parallel to dip. PI. 

 x, b, shows this character; here the flattened lenticular masses we call pebbles 

 are themselves gently folded with the rest of the rock. At the top of the 

 conglomerate this rock is overlain conformably by the Hoosac albite-schis. 

 series. At a distance of half a foot from the latter, thin bands of extremely 

 garnetiferous Hoosac schist alternate with bands of the fine grained con- 

 glomerates, forming a well marked transition. The rock at the -base of 

 the Hoosac schist group is extremely garnetiferous and of a dark, almost 

 black, dense character, with little feldspar. This garnetiferous character at 

 contact with the white gneiss is almost constant in this region and seems to 

 extend some distance above the contact, perhaps 50 or 100 feet; in the space 



