MOUNT GREYLOCK. 



157 



foliation, as such, may disappear altogether, becoming merged in the strati- 

 fication foliation. Thus, at the south end of 

 Ragged mountain, there is a minor syncline, 

 on the east side of which the cleavage has a 

 high easterly dip crossed by plications dipping 

 90°, or west, at high angle, while on the west 



. ,. . .j. . ,. ,. . Fig 59— Diagrams showing relation of 

 Side 01 tlllS syiiclllie the Stratification lOhatlOn cleavage to stratification in schist where both 

 nor 1 ]* l foliations dip in same direction; cleavage par- 

 fJlpS 25 to 30 east aild 110 QlStinCt cleavage allel to one or neither limb of plication. 



foliation is visible. (See Fig. 62.) 



PITCH. 



Early in the work my attention was directed by Prof. Pumpelly to 

 methods of detecting the pitch of the axes of folds. Observations of pitch 

 were made in fifty -four localities on Greylock, East, and Potter mountains. 



In a few places minor pitching folds are 

 exposed, as in the limestone at the south 

 base of Sugarloaf mountain (Fig. n'<»). 

 But pitch was usually determined by ob- 

 serving the pitch of the axes of the plica- 



Fra. 60.-Minor limestone folds with a northerly tiollS of any part of a fold. Tile angle 

 pitch, smith toot of Sngarloaf, STew Ashford. . , 



Rock 5ox3o feet. varies trom 5 to 45 , nut generally is not 



over 30°. In one or two instances it was over 45°. The correctness of 

 the method seems to be verified by the general parallelism which exists 

 between the minute and general structure of these rock masses, and also 

 by the opposite direction of the pitch as thus determined, at the extreme 

 ends of the mountain. 1 



STRUCTURAL PRINCIPLES. 



From the foregoing data the following structural principles may be 

 laid down as applicable primarily to the study of the metamorphic rocks of 

 Mount Greylock, and then to a large part of the Taconic region and to 

 similar rocks and regions. 



See, on the subject of pitch, Geo. H. Cook, Geology of New Jersey, Newark, X. .1.. 1868, p. 55; 

 on the inclination of the axes of the flexures in the Taeonic region, J. D. Dana, Taconic Rocks and 

 Stratigraphy, Part 2, p. 399, already cited. 



