192 GKEEN MOUNTAINS IX MASSACHUSETTS. 



78, 79.) The limestone area in the western part of the Bald mountain 

 spur is anticlinal in structure, but faulted. 



The relations which have been described above as existing between 

 the lower limestone (Stockbridge limestone) and the lower schist (Berk- 

 shire schist) are repeated at a higher level between the upper limestone 

 (Bellowspipe limestone) and the upper schist (Greylock schist). Ragged 

 mountain and the higher portions of the central ridge (Saddle Ball, Grey- 

 lock, Fitch, Williams) are synclinoria of the upper schist resting- upon and 

 surrounded by the upper limestone. The tongues and reentering angles and 

 isolated schist areas occur here, as well as in the lower formations. But the 

 isolated limestone area southwest of Cheshire, instead of being an anticline 

 of the Stockbridge limestone projecting through the Berkshire schist, seems 

 to be a syncline of the Bellowspipe limestone resting upon the Berkshire 

 schist, homologous to that which encircles and underlies Bagged mountain, 

 but without any similar mass of schist on it. The relative height of the 

 surface of the Farnham's quarry limestone, as shown in Section P, accords 

 well with this interpretation. 1 



RELATIONS OF GEOLOGY TO TOPOGRAPHY. 



It remains now to show the relations of the structural, lithologic, and 

 areal geology to the surface features. We find here evidence of the opera- 

 tion of several causes: 



First. The mineralogic character of the rock, presenting minerals more 

 or less easily disintegrated by physical or chemical agencies. 



Second. The internal structure and position of the strata, forming ele- 

 vations and depressions in the mass and determining the surface relations 

 of the different kinds of rocks. 



Third. Erosion, glacial, as well as pre-glacial and post-glacial, bringing 

 physical and chemical agencies to bear upon those irregularities in the form 

 and composition of the surface. 



1 These facts are brought out on the accompanying map and the sections (Pis. i, xviii-xxm). 

 Besides tin- usual dip and strike symbols there have been added on the map symbols indicating the. 

 direction and angle of pitch, and also the- symbols proposed by I>r. II. Keusch (op.cit.) to indicate 

 the cleavage dip and strike, and finally, numbers of the important localities referred to in this 

 report. 



