CORUNDIFEROUS NEPHELINE-SYENITE 439 
somewhat bent cords, having a little the look of apatite but with 
a small angle of extinction, perhaps tremolite. Occasionally 
decomposition products occur along fissures, having the appear- 
ance of kaolin but without any distinct structure. 
Scapolite is found in about a third of the sections, sometimes 
almost to the exclusion of other colorless ingredients and has 
the look of a primary mineral. Its anhedra meet the adjoining 
feldspar or nepheline in a sharply defined way with no hint of 
weathering in the latter minerals. Muscovite is a very common 
constitutent of these rocks, being found in more than half of 
the thin sections examined, generally as large primary looking 
individuals, sometimes associated with biotite though often with- 
out it. Biotite is practically the only dark mineral in the rock, 
hornblende not having been observed. As in the specimens 
examined by Adams, it is very dark in color and has a very 
small axial angle. Augite was found as small blue-green anhe- 
dra in one section only. Magnetite was not found, and apatite 
was rare. 
The most interesting accessory mineral is corundum, which 
sometimes occurs in fairly well formed barrel-shaped crystals 
half an inch in length, but is usually smaller and often forms 
only minute rounded grains. Its color is gray or less often pale 
bluish. Owing to the hardness of corundum it was found diff- 
cult to prepare sections rich in crystals and only two have been 
studied. Under the microscope their high refractive index and 
greater thickness than the rest of the section cause the corundum 
grains to stand out sharply. They are apt to be arranged in 
clusters in association with muscovite, often completely enclosed 
in at: 
Although the rock here described has a well marked schis- 
tose structure, there is nothing in its microscopic characters to 
suggest shearing or crushing, no mortar structure nor granula- 
tion, and seldom even undulatory extinction to hint at a state of 
strain. The rock as a whole is hypidiomorphic granular, and 
except corundum none of its constituents show much tendency 
to crystalline form. 
