Prrsson and Washington — Geology of New Hampshire. 347 



of Hitchcock, and they are so designated on the map. Where 

 we have seen them they are mostly gray micaceous gneisses 

 and mica schists. 



Geology of the main mass. — The greater part of the moun- 

 tain group is made up of a coarse-grained hornblende syenite, 

 a hornblende-grano-jndaskose in the new classification, whose 

 characters will be given in a succeeding petrographical paper. 

 It is this rock which composes the mass of Mt. Gunstock, of 

 Mt. Belknap the peak next north of it and of the northern 

 extension in Locke's Hill. It occurs also in the ledges exposed 

 on the higher part of the road from Gilford to West Alton, 

 where it crosses over the mountain. It also forms the higher 

 parts of Piper Mountain south of Gunstock Peak, and it runs 

 over towards Mt. Straightback. In Piper Mountain it assumes 

 a somewhat porphyritic character. It is seen on the sides and 

 cresrs of the main elevations in massive outcrops and exposures 

 often several hundred feet across and is thus thoroughly laid 

 bare. These surfaces show everywhere the planing and 

 smoothing of glaciation. In none of them did we find the 

 rock perfectly firm and unchanged. Everywhere its color 

 ranges from a reddish to brownish, it tends to crumble under 

 the hammer and in places it is loose and crumbling into coarse 

 gravel. The chemical analysis shows however that this is not 

 due to any chemical alteration of the constituent minerals, but 

 to mechanical disintegration from the action of frost and 

 weathering, which have tended to loosen the texture of the 

 rock. Blasting would probably reveal excellent material at a 

 few feet below the surface. We did not find any quarry open- 

 ings in this rock-material ; it is in general too high above the 

 zone of cultivation to have made such work necessary. In 

 only one place did we find this type at the contact zone against 

 the older rocks, on the southwest slope of Locke's Hill in a 

 little ravine where it is in contact with mica schist. It is here 

 rather coarse, altered and not of typical composition. 



Contact fades of fine-grained granite. — With the exception 

 just mentioned, in all localities examined by as, we have 

 found that at the contact with the enclosing rocks, not the 

 syenite but a fine-grained granite {grano-liy arose) is present. 

 The lower slopes where the actual contact lies are in general 

 so covered with glacial drift and soil, often with a more or less 

 dense growth of vegetation, that it is masked and rarely seen, 

 but immediately above where it should be this granite appears 

 and beyond and above it the syenite. This we found to be the 

 case in a number of places on different sides of the mass, so 

 for example at the west foot of Mt. Gunstock, the west and 

 south slopes of Piper Mountain, the northeast foot of Locke's 

 Hill, at West Alton and on the southern prolongation of the 



