1 6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 



westerly section between Shepaug and Bantam Rivers was holed 

 through in April, 1926, and the easterly section was holed through 

 in September of the same year. For much of the way the rock 

 strata was found so solid or so interlocked as to make it unneces- 

 sary to support the roof, either temporarily or permanently. A 

 singularly small amount of water was encountered, even where for 

 more than a mile the tunnel penetrated under Bantam Lake and its 

 basin. No especially troublesome faults were found. 



General Geology 



The region is underlain by igneous and metamorphic rocks that 

 comprise two schist series ; a diorite intrusion, in part gneissic ; a 

 hornblende gneiss ; and still younger granite and pegmatite intru- 

 sions. 



The two schists, the Berkshire and the Hartland, are the oldest 

 rocks of the region. They are quite distinct in the field and are 

 not believed to be of like age. They lie next to each other in 

 many places but occur in discontinuous, scattered outcrops with- 

 out any visible contact and, unluckily, the tunnel cuts through 

 an area where the two are separated by several miles of diorite, 

 intrusive into both. 



The legend attached to the accompanying map does not assign 

 any definite geological age to the formations exposed in this 

 area. It is thought best to place the rocks in their relative posi- 

 tions according to the structural and petrographic evidence in the 

 region and to await dating the series until work in the surrounding 

 regions affords more convincing evidence than any on hand at 

 present. The map is taken from the Litchfield Quadrangle, 

 Conn.-N.Y., pubHshed by the United States Geological Survey. 



In 1894 R. Pumpelly^ made the Hoosac schist, on the east flank 

 of Hoosac Mountain, equivalent to the whole of the Stockbridge 

 limestone, Berkshire schist. Bellows-pipe limestone, and part at 

 least of the Greylock schist lying west of that same mountain. 

 Pumpelly^ believed he had evidence that the Stockbridge limestone 

 graded laterally into the Hoosac schist along the western base of 

 Hoosac Mountain and in the valley of the Hoosic River. The 

 Cambrian Vermont formation and the pre-Cambrian Stamford 

 gneiss underlie the Hoosac schist and compose the core of the 

 Mountain. 



The Hoosac Mountain ridge marks the beginning of the Green 

 Mountain anticlinorium in Massachusetts, an elevated plateau that 

 extends north and south through the western part of the State and 

 separates the lowland of the Connecticut River on the east from 

 the Housatonic Valley on the west. The plateau is composed of 



^ Geology of the Green Mountains in Massachusetts, by Raphael Pumpelly, T. Nelson 

 Dale, and J. E. Wolff, U. S. G. S. Monograph 23, 1894. 

 ' Op. cit. pp. I4-I7. 



