262 Pirsson and Washington — Geology of Red Hill, JV. H. 



shredded out, is that of ordinary granite and commonly con- 

 tains small zircons surrounded by pleochroic halos. The mus- 

 covite appears chiefly in the feldspars and along cleavage 

 cracks and is clearly an alteration product, though not distinctly 

 in the sericitic form. Apatite crystals of the ordinary kind 

 occur. 



Although as stated, the gneiss has not been made the object 

 of especial study, and not enough is known about it to warrant 

 definite conclusions as to its origin and character, from what has 

 been seen, combined with the facts mentioned above, it would 

 seem very probable that it is an ordinary biotite-granite which 

 has suffered dynamic shearing from which, with little or no 

 recrystallization, it has assumed the gneissoid structure. 



Contact Fades of the Syenite. — The actual contact of the 

 gneiss and the syenite is practically everywhere hidden by 

 debris and glacial drift. Hitchcock mentions one locality 

 where it may be seen, as previously stated, but this was not 

 found by the writer. In a number of places, however, and 

 especially at the foot of the eastern slopes, in the pasture fields, 

 the contact can be carried to within a few yards, notably at 

 one point just south of a little cemetery where many expo- 

 sures of the bed rock are seen. Here, about 200 feet above 

 the road, the gneiss is full of seams, patches, and dikes of peg- 

 matitic alkali-feldspar, which change within short distances to 

 aplitic dikes. In addition to the feldspathic dikes there are 

 also many of dark-colored trap-like ones filling narrow frac- 

 tures in the gneiss and trending outwards in directions gener- 

 ally normal to the plane of contact. Immediately above this 

 the syenite is in place ; it is fine-grained and quartzose ; as one 

 follows it up the slope it becomes coarser in grain and eventu- 

 ally assumes the normal type of the massif. Precisely similar 

 phenomena were found at the foot of the eastern slopes of the 

 north peak, where heavy outcropping ledges in the fields give 

 good exposures, and again at the north end of the mountain. 

 The gneiss is filled with aplitic dikes, often only a few inches 

 wide, which run in various directions and frequently anasta- 

 mose. There are also the same lamprophyric dikes and the 

 general trend, of the larger dikes is away from the peak. 



Near the contact the syenite is very fine-grained, becoming 

 coarser at a distance. These endomorphic changes in it will 

 be more fully described and discussed in the following petro- 

 graphic part of this work : it is sufficient to say here that the 

 facts mentioned above indicate very clearly that the gneiss is 

 the older rock, through which the syenite has broken up and 

 against which it has distinct contact phenomena. 



The Central Syenite. — The petrographic description of this 

 rock will be given later, but a few facts in regard to its geo- 



