154 



GREEN MOUNTAINS IX MASSACHUSETTS. 



carried too far, however, for local changes may occur for a brief space in the 

 direction of the plications and of the cleavage foliation, owing to the pres- 

 ence of quartz nodules; or there may also be minor undulations on the side 

 of a great fold. 



Fig. 54.— Specimen of .schist from locality 539. about one-quarter mile southwest of Greylock summit, in its natural 

 position, facing sooth. Stratification nearly liorizontal; cleavage dip 5U"-55° east. From a photograph. 



The above cases are sufficient to illustrate the structural significance 

 of stratification and cleavage and the distinction between them in the region 

 under investigation. With the aid of these a fault was detected which 



would otherwise have escaped notice. Near 

 the west end of the Bald mountain spur there 

 is a somewhat lenticular area of limestone 

 trending north and south, and in contact on 

 both sides with schist. On the west side the 

 contact phenomena are as indicated in Fig. 

 55. The limestone overlying the schist dips 

 fn mi 45°-60° east, the contact plane between 

 both 55° east: the schist cleavage dips 25°- 

 55° east, but the plications in the schist dip 

 west at a somewhat higher angle. The nor- 

 mal position of this limestone is under the schist; here it is above in conse- 

 quence of a fault. At this point the stratification foliation in the schist is 

 very much plicated, and the cleavage faulting divides up the rock into lens 



" Fig. 55.-=-Diagram showing the relations of 

 the Berkshire schist and Stockbridge limestone 

 nt locality 576, cm the Bald Mountain spur, look 

 ing north. The cleavage of the schist conforms 

 to the stratification of the limestone, but the 

 stratifications are unconformable. 



