20 GREEN MOUNTAINS IN MASSACHUSETTS. 



strata that it is impossible to give the real vertical dimensions. His 

 estimate is: 



Greylock schist 1, 500-2, 000 



Bellowspipe limestone 000- 700 



Berkshire schist 1, 000-1'. 000 



Stockbridge limestone 1, 200-1, 400 



These are, however, based on measurements of beds that have been 

 subjected to strong lateral compression, and, as Mr. Dale observes, although 

 the aggregate maximum of the thickness given above is below that assigned 

 to the Lower Silurian in the Appalachian region, it is probably far in excess 

 of the real thickness, which maybe considerably below the maximum above 

 given. 



The sediments which in vast thickness form the substance of the Green 

 mountain system have been subjected to intense lateral thrust, which has 

 produced numerous folds. These, as a rule, are more or less compressed 

 and overturned to the west, in places indeed forced over until the axial 

 plane lies almost horizontally, or compensations have taken place through 

 overfaulting. The sections and map of the Hoosac-Greylock region illus- 

 trate the structure in its generality. 



From these it will be seen that on Hoosac mountain the granitoid 

 gneiss and the overlying conglomerate gneiss-quartzite and albitic schists 

 have been folded into a low anticlinal arch, the western side of which has 

 been forced over to form an overfold to the west. 



An examination of the longitudinal sections on Plate vi accompanying 

 Part ii (Mr. Wolff's report) shows that the southern end of this arch is over- 

 folded in the same manner, but to the south. We have thus the remarkable 

 occurrence of an overturned anticline abruptly turning a right angle. A 

 glance at the map (Plate n) will show that this is repeated by the next over- 

 folded anticline to the west, which bends equally abruptly around to run 

 eastward, and that the inverted trough between these anticlines is still 

 marked by the infolded hand of schist. Going from this southward, we 

 come immediately upon another east and west trough of schist, also over- 

 turned to the south. Still further southwest, we find along the northern 

 part of the Dalton- Windsor hills the quartzite gneiss beds thrown into 



