HOOSAC MOUNTAIN. 69 



One vertical dike of this rock at Stamford, Vermont, contains blue 

 quartz grains and broken crystals of microcline, which have been taken from 

 the country rock of the dike, the granitoid gneiss (Stamford granite). 



GEOLOGY. 



For convenience of description the region covered by the map (PI. i) 

 may be divided as follows: 



First. The Hoosac tunnel. 



Second. The region embracing the central part of Hoosac mountain 

 from the tunnel line on the north to the point in Cheshire where the cresi 

 of the mountain makes an offset to the west. 



Third. The area covered by the schists occupying the northern and 

 eartern parts of the map. 



Fourth. The region south of Cheshire and of the Hoosic valley. 



Fifth. Hoosic valley schist. 



Sixth. The region around Clarksburg mountain and Stamford, Vermont. 



THE HOOSAC TUNNEL. 



This great engineering- work is 4| miles long, entering the base of 

 Hoosac mountain from the Hoosic valley on the west, and running in a 

 nearly due east direction across the trend of the range. Two shafts have 

 been sunk; the deepest, the central shaft, near the center of the tunnel, is 

 about 1,000 feet deep, descending from the basin-like depression on top of 

 the mountain. (See PI. v, Profile iu). The other, the west shaft, is not 

 quite half a mile from the west portal, and is 325 tret deep. About 1,000 

 feet west of the west shaft, a small shaft called the "well" was sunk, on the 

 dump of which specimens of the rock are found. 



The tunnel itself is a large double-track opening, which, starting from 

 the Stockbridge limestone at the west portal, passes through all the rocks 

 of the series at least once. But several things combine to greatly lessen its 

 value as a geological section of the core of the mountain. A considerable 

 proportion of the tunnel is now bricked over, and only in the manholes, 

 every 250 feet, can the ruck be seen; and secondly, the covering of soot 

 and smoke on the rock is very thick, making it necessary to get fresh sur- 

 faces by hammering. The difficulties of working by lamplight in the smoke 



