No. 40] GEOLOGY OF SHEPAUG TUNNEL 1 7 



pre-Cambrian rocks flanked on the east by the Hoosac schist over- 

 lain by the Rowe schist, and on the west by the Dalton formation, 

 the Cheshire quartzite, the Stockbridge limestone, and the Berk- 

 shire schist. The Stockbridge limestone is the valley formation of 

 the Housatonic lov^land. The Cheshire and Dalton lie as isolated 

 patches along the border of the upland or project into it as spurs 

 and, together with the Berkshire schist, form the isolated hills that 

 rise above the valley floor. This area has been the subject of a 

 number of papers by B. K. Emerson, culminating in "The Geology 

 of Massachusetts and Rhode Island," published in 191 7 as Bulletin 

 597 of the United States Geological Survey. In the correlation 

 tables facing page 17 the Hoosac schist and Rowe schist are made 

 the equivalent of the Berkshire — all of Ordovician age. That is, 

 the Hoosac is taken entirely out of the Cambrian and much 

 restricted in the Ordovician. 



The Green Mountain anticlinorium enters northwestern Con- 

 necticut as the Norfolk Hills and passes out of the State into 

 southeastern New York as a belt of highlands including Barrack 

 Mountain, Cream Hill, and Sharon Mountain. It is intersected 

 by the Housatonic River which leaves the westerly swinging lime- 

 stone valley to cross the highlands in a narrow north-south gorge. 



The Hoosac schist passes down into Connecticut as a continuous 

 strip of varying width lying along the eastern edge of this anti- 

 clinorium and is known as the Hartland schist.^ The Dalton 

 formation, the Cheshire quartzite, Stockbridge limestone and Berk- 

 shire schist maintain their position on the west of the axis until 

 the latter swings southwest out of the State. At this point the 

 supposedly younger series bridges the pre-Cambrian plateau and 

 the Berkshire schist is widely developed in the hills of Cornwall 

 and Kent and comes into contact with the Hartland schist in the 

 neighborhood of Litchfield. The Cheshire quartzite and the 

 Stockbridge limestone are also at present^ represented as occurring 

 south of the plateau in long narrow bands though there is con- 

 siderable doubt concerning the equivalence of these to the forma- 

 tions north of the plateau. 



A word must be included here concerning the Berkshire forma- 

 tion as it is now mapped in Connecticut. (See reference above.) 

 It forms at least two very distinct types, namely, that on the Mount 

 Washington range, the extension of the Taconic Mountains into 

 Connecticut, a greenish sericite, chlorite schist with considerable 

 albite and local development of garnet ; and the Canaan Mountain 

 type, a quartz, biotite schist or a gneiss with as much as ten per 

 cent of oligoclase and considerable amounts of garnet, staurolite 



1 The Hartland schist may represent in part the Rowe schist of Massachusetts that 

 overlies the Hoosac. It is tentatively considered here as being equivalent to the Hoosac 

 as stated by Rice & Gregory, Manual of the Geology of Conn., Conn. Geol. & Nat. Hist. 

 Survey, Bull. 6, 1906. 



2 H. E. Gregory and H. H. Robinson, Preliminary Geological Map of Connecticut, 

 Bulletin No. 7, Connecticut Geological and Natural History Survey, 1907. 



