HOOSAC MOUNTAIN. 87 



continues for some distance to have its northerly pitch, but small folds begin 

 to come in, as for instance in Profile in, PI. v, parallel to the tunnel line, on 

 the west summit of the mountain, where a small syncline exists. Note in 

 this profile on the west slope of the mountain how the clips roll from east to 

 west with commonly a northerly pitch. It is characteristic of this rock 

 that it forms gorges and waterfalls along the side of the mountain. Hoosac 

 mountain presents an unbroken wall for 12 miles in Massachusetts, extend-- 

 ing into Vermont, Profile i, PI. v, gives one of the best sections through 

 the schist; it extends from the valley to the summit of Hoosac mountain and 

 shows the structure here by an almost continuous section. On the slope of 

 the mountain proper, the rocks have a gentle easterly dip, while at the base 

 there is considerable rolling. On top of the mountain there is again a gentle 

 rolling of the rocks. 



The west end of Profile i is separated by a shallow, drift-covered 

 depression a few hundred yards wide from a long north and south ridge in 

 the valley (see map) on the summit and sides of which we find the typical 

 Hoosac albite schist, often very garnetiferous, extending in an almost straight 

 line to near the western portal of the tunnel, where it stops. This ridge of 

 schist is everywhere separated from that of Hoosac mountain by this small, 

 drift-covered hollow, so that we have only the lithological identity to cor- 

 relate by. This rock is succeeded by the limestone on the west throughout 

 its extent. Profile n, PI. v, shows the relations of the rocks across this 

 ridge, beginning with those which are exposed on the north fork of the 

 Hoosic river in North Adams. The Stockbridge limestone lias here its most 

 northern outcrop in Hoosic valley and strikes north 20° east, the dip varies 

 considerably; the rock is much folded, a fact well shown in a quarry and 

 chasm in the limestone at the "Natural Bridge." This rock is succeeded 

 within 60 feet by a schist with conformable strike, and dip east 40°. About 

 800 feet across the strike east from this contact, with one or two intervening 

 outcrops of schist, we have a high bluff along the river, composed of mica- 

 ceous schistose limestone, effervescing strongly with acid, striking north 25° 

 east and dipping 25° east. This bluff extends for some distance and is 70 

 feet high, exposing a considerable thickness of the rock. At the top of the 

 bluff there is a flat bench, gently rising to the east (evidently formed by 



