2 JOSEPH H. PERRY ' 



closer study of the map and of the mountain from different 

 sides, it is seen to consist of two well-defined parts. There is a 

 northeast-southwest ridge, about six miles in length, extending 

 from the center of Dublin to Gap Mountain. This constitutes 

 the eastern part of Monadnock. This ridge rises by a succession 

 of steps from an elevation of 1,500 feet at its northern extremity 

 to 2,800 or 2,900 at its culmination east of the summit of the 

 mountain, and then descends by a like succession of steps to 

 its southern extremity. 



The eastern slope of this ridge above the foothills is quite 

 steep, even precipitous. The western part of the mountain, 

 which includes the summit, rising 300-400 feet above the eastern 

 ridge, consists of a single peak set, as it were, in the central 

 part of the western slope of the ridge. The northwest slope of 

 this peak is gentle ; the west and southwest slopes are much 

 steeper; while the northeast slope meets the northern half of 

 the western slope of the ridge forming the valley of Mountain 

 Brook. These divisions and their slopes are closely related to 

 the underlying rock structure, and indicate that erosion is con- 

 trolled or guided by this structure. 



The rock of this mountain is a banded mica schist, the band- 

 ing being generally parallel to the present structure. The schist 

 presents three marked variations. In the top of the mountain 

 and in the upper part of the eastern ridge it is a gray, massive, 

 garnetiferous, biotite, sericite schist, in which the biotite is 

 specially noticeable because of its arrangement in bright, 

 isolated scales, one-sixteenth of an inch in diameter, set in a 

 fine, light gray groundmass.^ In addition, andalusite crystals, 

 or what were once andalusite crystals, occur in this schist, some- 

 times very abundantly, lying parallel to the present structure of 

 the rock. The accompanying picture (Fig. 2) shows how 

 abundantly these may occur in the schist. They are frequently 

 five or six inches long by half an inch, or more, through. Owing 

 to the unequal weathering, these prisms frequently appear in 

 relief on the surface of the ledges. In the southern half of the 



'In the Geology of New Hampshire this schist is called the Kearsarge andalusite 

 schist. 



