380 



unaffected by the contact are orthoclase and zircon. This fact shows 

 that when the granitic magma reached its present position the two 

 latter minerals were present in it as crystals. 



The sedimentary rock is described as a dark "argillitic mica- schist." 

 It occasionally contains crystals of andalusite which, however, do not 

 appear to have anything to do with the granite. At a distance of 100 feet 

 from the junction the only visible crystals are the rare andalusite crystals, 

 unless the glistening aspect of the surface be regarded as indicating the 

 presence of mica. Microscopic examination shows that this schist or 

 micaceous clay-slate is essentially composed of quartz, white mica (sericite) 

 and chlorite. It contains also titanic iron partially changed to leucoxene, 

 magnetic iron and probably carbonaceous matter or graphite. Biotite 

 and tourmaline occur only as accessories. At 50 feet from the junction 

 no change can be observed. At 25 feet the rock is more decidedly crystal- 

 line, and biotite and tourmaline (blue within and brown without) are more 

 abundant. From this point inward the change is very rapid. At 1 5 feet 

 the rock is still schistose but hard, much fractured and full of shining dots, 

 which indicate a new crystalline development. Biotite has increased at the 

 expense of the original chlorite, and there is much tourmaline. Between 

 this point and the contact the rock loses all traces of schistosity and 

 becomes a black hornstone which breaks into small angular fragments. 

 At 10 feet the rock gives a qualitative reaction for boron. Up to this 

 point it has been growing coarser, now it grows finer and passes into a 

 compact flinty hornstone, composed of quartz, biotite, tourmaline and iron 

 oxide. Between the hornstone and the granite there occurs a band, scarcely 

 recognizable at the top of Mt. Willard, but becoming wider as it is traced 

 downwards, composed of a dark grey substance which is traversed in all 

 directions by reticulated black veins. This band is composed essentially 

 of tourmaline and quartz. The tourmaline, unlike that of the hornstone, 

 occurs in idiomorphic crystals and often shows the most exquisite zonal 

 banding. The rock of this band is termed tourmaline- veinstone by HAWES. 

 It answers to the tourmaline-quartz-brochenfels of German authors. The 

 following analyses illustrate the variation in composition in one and the 

 same bed: 



Si0 2 



A1A ... 



Fe.,0 3 



FeO 



MnO 



CaO 



MgO 



K 2 



Na 2 



Ti0 2 



B 2 3 



Fl 



H 2 



100-61 100-49 100-05 101-20 100-78 100-73 

 Sp, Gr. ... 2-85 2-84 2-82 2'74 2' 78 2-65 



