80 GKEEN MOUNTAINS IN MASSACHUSETTS. 



to a northwest strike and northerly dip — that is, the la vers circle around 

 in the space of a few hundred feet, giving- a canoe-shaped fold. The 

 development of the very large porphyritic feldspars just in the turn is also 

 significant. In short, this space, so marked topographically, is the place 

 where part of the layers of the white gneiss are crumpled and pinched 

 together in the extreme point of the great fold which we have been describ- 

 ing. It will be seen from what has been said that the central part and 

 crest of lloosac mountain is composed of a great, anticlinal fold in the three 

 members of the series — granitoid gneiss (Stamford gneiss), metamorpbic 

 conglomerate (Vermont formation), and albite-schist (Hoosac schist) — and 

 that this fold has a pitch or inclination of its axis of 10° to 15° to the 

 northward, while the western side has been pushed in under or overturned, 

 this overturn continuing into the southwestern part. The beds are in 

 inverted order on the west and southwest sides: in normal order on the 

 north and east sides. By reason of the pitch of the axis the same rock 

 occurs in the tunnel, 1 mile north of the last appearance of the granitoid 

 gneiss on the surface, flanked on both sides by the conglomerate and 

 albite-schist; these two formations on the east side dipping east, overlying 

 the granitoid gneiss in normal order On the west we find the same transi- 

 tions between granitoid gneiss and white gneiss-conglomerate that were 

 observed on the surface, and a nearly vertical structure. Profiles x and 

 xii. PI. v, give these relations graphically. 



The belt of Hoosac schist which is seen on the map to run around 

 the central gneiss and nearly to join the great mass of schist on the east, 

 starts off from the main mass as a broad tongue, narrowing rapidly to a 

 small constant width. At various points its top and bottom contacts with 

 the gneiss on either side have been observed. Over the tunnel this schist 

 can not be found in definite contact with the western gneiss; on the con- 

 trarv, there is a gradual transition, which can be seen in the outcrops on 

 the slope of the mountain above the west shaft. We hardly find here in 

 the schist what we can call a dip of any kind — simply the usual fluting, 

 with the strong northerly pitch of the axes. Following the band down to 

 a point some hundred yards north of Profile iv a , PI. v, we find here the east 

 contact of the schist and white gneiss. The schist is very garnetiferous, as 



