LITHOLOGY. 223 
color and in proportion of ingredients; but I think this description may 
be regarded as representing them all fairly. This is the novaculite, or 
oil-stone, that is so highly prized for sharpening tools. 
QUARTZ SCHIST (QUARTZITE). 
Almost all kinds of schists, by the elimination of the minerals which 
characterize them, graduate into quartz schist. Very siliceous varieties 
of mica schist, argillitic schist, chlorite schist, etc., stand between quartz 
schist and these various rocks; and therefore this rock, which typically 
is a pure schistose mass of quartz, possesses a variety of characters that 
are given to it by its accessories, and which relate it to other rocks 
that have been and are to be described. The rocks abound in the Con- 
necticut valley and geologically related areas. They show very various 
degrees of metamorphism; and although, as a rule, their structure indi- 
cates a complete recrystallization of the materials that formed the sedi- 
mentary beds, still cases are not wanting where remains of the frag- 
mental character are maintained. It is understood, that in this place the 
rocks with the latter character are not considered, but are included 
among the descriptions of half fragmental rocks that follow. In texture, 
all grades occur between coarse granular and cryptocrystalline varieties ; 
and in structure, all grades between very schistose and almost massive 
rocks. 
The most common kind of quartz schist is micaceous. A white mass, 
consisting of granular quartz, shows on its schistose cleavages flakes of 
a glistening mica, which is usually all muscovite, and rarely is partially 
biotite. This is in contrast to most of the micaceous rocks; for though 
a little alumina and potash may remain, usually but little iron exists 
in such highly siliceous sediments. The reverse is, however, shown by 
a specimen from Newcastle, in which a very fine-grained quartzite is 
traversed by multitudes of black, parallel lines, which on investigation 
are found to be made by the arrangement of minute grains of magnetite. 
ad micaceous quartz schist from Hinsdale is composed of a very pretty 
bluish Epaleseen quarts and its mica is more fibrous than foliated. In 
Shite other varieties, the presence of mica is only indicated by that glis- 
tening lustre that characterizes the argillitic mica schists, 
