GENERAL STRUCTURE AND CORRELATION. 17 



northern end simply the Berkshire schist resting upon the Stockbridge 

 limestone, while as we go southward we find it representing not only the 

 Berkshire schist, but also the whole thickness of the limestone itself, and as 

 we go eastward we find through continuous exposures its connection and 

 identity with the tongues of schist infolded in the Cambrian quartzite 

 •gneiss of Hoosac mountain. 



In Fig. f) I have attempted to represent, in a somewhat ideal section, 

 the transition from limestone to schist at the south end of the Cheshire hill. 

 The transition is clearly quite abrupt, 

 and might easily occur within the space 

 represented l>v the eroded folded arch 

 between the limestone and the infolded 

 schist along the west base of Hoosac 



£, ... Fig. 5.— Ideal section east of Cheshire, showing 



mOUlltam. r>ee C, I 1. HI. lateral transition of limestone to Hoosac schist; S, 



r p. _ _ 1 T Berkshire schist ; L, Stockbridgelimestone <j>, Lower 



1 lie Western end (it tile HoOSaC tUll- Cambrian quartzite of Dalton-Windsor hills; Cq, cal- 



wu»i>d quartziti-: transition quartzite to limestone; 

 lie! lies 111 tile belt 01 tlllS lateral tranSl- OS, calcareous feldapathic schist in lateral transition 

 . » i < i i • l i* • i from Stockbridge limestone to Hoosac schist. 



tion ot the Stockbridge limestone into the 



Hoosac schists; but it is now completely hidden by the brick arching ren- 

 dered necessary by the decomposed condition of the material. Indeed, it 

 acted for several hundred yards from the portal as a quicksand, and the 

 tunneling work had to be preceded by small tunnels incased in closely 

 matched planks, so fluid was the decomposed water-saturated rock. 1 have 

 attempted to represent the structural facts at this point on the west flank of 

 Hoosac mountain in d, PI. in. 



At the time of my examination of the tunnel, in 1865, the limestone 

 was exposed in open cuts and tunnels — nearly parallel to the present open 

 cut — for nearly 700 feet east and west. The exposure showed in this dis- 

 tance two rather flat anticlines. The eastern limb of the easternmost anti- 

 cline dipped east and was for a short distance concealed by masonry. East 

 of this was an open cut, for nearly 400 feet, in the decomposed rotten schist, 

 which seemed to show faintly preserved indications of an easterly dip. 

 Just east of the middle of the cut a less altered bed showed a well-defined 

 syncline with an anticline on the east and having the eastern limb of the 



latter exposed in the heading with easterly dipping structure. 

 mon xxiii 2 



