352 Pirsson and Washington — Geology of New Hampshire. 



of persalic rock. While in the crest of the ridges and in the 

 peaks these dikes vary in texture from dense felsitic to sugar 

 granular granites, in the contact zone we observed only the 

 latter, and they sometimes pass into varieties with pegmatoid 

 texture. 



With only a few exceptions all of these occurrences are on 

 too small a scale to be shown on the map. The salfemane 

 dikes were not nearly so numerous, but on account of the con- 

 trast made by their dark color appear more distinctly defined. 

 They were also observed cutting the exposed rock surfaces on 

 the tops of the mountains ; there are several below the summit 

 of Mt. Belknap on the southwest side and one six feet wide 

 with porphyritic feldspars cuts the very highest point of the 

 peak with east and west trend. Three or four of about the 

 same size were found on the top of Mt. Gunstock and they 

 were likewise observed on the crest of Mt. Piper. The 

 lower slopes of the mountains are probably cut by them also, 

 but the masses of debris and vegetation which cover them hide 

 the exposures in which they might be seen. 



They occur also in the surrounding rock masses in which the 

 intrusion took place. Here again the exposures are difficult to 

 find, but one place, Sander's Neck, a small promontory on the 

 shore of the lake north of the mountains, presents considerable 

 areas of the glaciated gneisses, and these we found traversed 

 by several intersecting dikes of these salfemic rocks. As usual 

 they were but a few feet in width. They occur in the mica 

 schists which are exposed at the foot of the lower west slopes 

 of Mt. Gunstock and Mt. Piper, and from what we have 

 observed around the similar intrusive mass of Red Hill north 

 of the lake, it seems probable that a more detailed study of the 

 surrounding region would show a considerable number of them 

 extending to relatively long distances from the central parent 

 mass. Some of those mentioned above are shown on the 

 accompanying map. 



New Haven, Conn., and Locust, N. J., May, 1905. 



