MOUNT GREYLOCK. 



151 



those localities, is also northeast. A large ledge of schist at Readsboro, 

 in Vermont, in the Green mountain range (Fig. 51), shows oh a large scale 

 the two sets of foliations and quartz lamina', with different strikes and dips, 

 and will serve to illustrate what is not uncommon on Greylock in similar 

 rocks. 



The parallelism between the strike of the cleavage and the strike of 

 the axis of the great folds has 

 long been recognized in geology 

 When, therefore, the axis of the 

 fold lies horizontally the strike of 

 the sides of the fold will conform 

 to the strike of the cleavage; but 

 when the axis of the fold is in- 

 clined, i. e., when the fold pitches, 

 the strike of the sides of the fold 



Fig. 51.— Sketch of west side of schist ledge in Readsboro 

 Will not conform to that Of the "^g 6 - vt - ""towing stratification striking K. 20° E., and dip- 

 ping 25° west, crossed by cleavage striking N. 15 c \V . and dip- 

 Clekvaffe. This Pl'of. Pumpelly ping 55° east, with quartz lamina? in both foliations. As the 

 ° 1 . ta ,, 6 of i e( j ge ; s llot p ara n e i w itb the strike of either foliation 



Suggests, is the mOSt probable ex- the apparent angles of dip are not the true ones. 



planatioii of these differences between the strikes of the stratification and 

 cleavage. The conformity which Heim finds in the Alps between the 

 strikes of the two foliations does not hold here. 1 



CASK VIII. 



Ill Goodell hollow, locality 175, southwest of Bald mountain, there is 

 a schist with three sets of planes or foliations, set a striking north . r )° east, 

 and dipping 35° to 4."> east; set b striking north 20° east, and dipping 40° 

 east; set c striking north 80° east, and dipping 70° north. An enlarged 

 thin section (Fig. 52) shows that the minute plications follow the direction 

 of set b, while set a is formed by a slip cleavage more or less pronounced, 

 and set c by the infiltration of dark mineral matter in planes, possibly 

 fractures, traversing the other two sets without altering their structure. 

 This interpretation of this locality is also confirmed by the strikes and dips 

 observed in its vicinity. At locality 132, near the west end and on the 



1 Sec his law 13, op. c i t . , vol. 2, p. ti8. 



