MOUNT GKEYLOCK. 



153 



tion. Tlie same stratification foliation and cleavage foliation dips recur at 

 locality 549, some 2,500 feet south-southeast, and at locality 539 (see Fig\54) 

 about 1,000 feet west, and again at the top of Greylock, and may thus be said 

 to characterize the entire eastern portion of the summit of the mountain. If, 

 therefore, the larger microscopic specimen in Fig. 53, which only measures 

 1£ Dv i inches, be properly oriented it will correctly represent the structure 

 of an area measuring about two-thirds of a square mile, and probably the 

 entire east side of the highest syncline of the Greylock mass. (See Sec- 

 tions g, H, i, PI. xx.) 



■8K1 



Fig. 53. — Thin section of sericite-chlorite-schist from locality C>">0, about one-quarter mile south of Greylock summit. 

 enlarged 2\ diameters, showing a coarse slip cleavage crossing a very minutely plicated stratification. In preparing the 

 slide fractures occurred net inly in the direction of The cleavage, here the direction of least resistance. From a photograph. 



The microscopic structure thus often epitomizes the general structure 

 on one side of a fold. This fact agrees with the drift of what Mr. Heim 

 implies in regard to the structure of the Toedi-Windgaellen-Gruppe namely, 

 that physical causes have transformed great masses by transforming the 

 minute particles which constitute them. 1 This generalization must not be 



1 Op. lit., vol. ii, p. 99. 



