PRIMARY ROCKS. 
71 
is very ambiguous. Primitive rocks occur either as 
protruded masses, as overlapping masses, resulting 
from the spread of matter after ejection, or as vein- 
stones, filUng fissures, apparently consequent on 
some violence to which the strata have been sub- 
jected." 
Primary rocks are chiefly composed of the hard 
minerals, quartz, feldspar^ and hornblende; mica and 
talc are disseminated in smaller proportions, and 
limestone and serpentine occur in beds or masses, 
but less frequently than the above-named minerals. 
CLASS I. 
Primary Rocks, 
1. Granite. 2. Gneiss. 3. Mica Slate. 
Subordinate Rocks which occur among Primary. 
1. Hornblende Rock. I 3. Crystalline Limestone. 
2. Serpentine. | 4. Quartz Rock. 
Some of these subordinate rocks occur also among 
transition rocks. Bake well justly remarks, that gran- 
ite, gneiss, and mica slate might with propriety be 
regarded as belonging to one formation, as they 
are essentially composed of the same minerals, vary- 
ing in different proportions, and, accordingly, are 
rather modes of the same rock than different spe- 
cies. We often, indeed, see them passing into each 
other, as one of their constituent minerals becomes 
more or less abundant. 
Granite, 
Granite is a compound rock, composed of quartz^ 
feldspar, and mica, arranged in various proportions, 
and varying accordingly the aspect of the mineral. 
The crystals of each may be large or small ; in one 
portion of the rock equally mixed ; in another, un- 
equally blended ; so that we often find the quartz or 
