CHAPTER A, 
ROCKS—continued 
Metamorphic Rocks—A. Schistose Rocks, their General Characters. 
Quartzose Rocks. Argillaceous Rocks. Mica-schist. Gneiss. 
Chlorite-schist. Talc-schist. Amphibolites. Granulite. Marble. 
Serpentine. &. Cataclastic Rocks, their General Characters. 
Mylonites, Friction-breccias. Determination of Rocks in the Field. 
General Characters of Argillaceous, Calcareous, Siliceous, and Fels- 
pathic Rocks. Specific Gravity of Rocks. 
III. METAMORPHIC ROCKS 
A. Schistose Rocks 
THE rocks ofthis great class are for the mostijga 
crystalline, and characterised by the structure known as 
foliation. Ina foliated rock or schzs¢ the constituent minerals, 
which may consist of one or of several species, are arranged 
in more or less parallel layers. Each layer may be composed 
of one kind of mineral only, or two or more different kinds 
may be commingled. The layers or folia are usually 
lenticular in form—in some cases being remarkably even and 
parallel, so as to give the rock an appearance as of fine 
lamination (see Plate XXII. 2). In other cases the individual 
folia thicken- and thin-out rapidly (see Plate XXIII.), alter- 
nate irregularly, are often undulating, and frequently crumpled 
and puckered. The several folia are not as a rule readily 
separated from each other—the minerals of one being usually 
more or less closely intermingled, felted, and welded with 
those of adjacent layers (see Plate XXI. 1, 2). In all these 
respects the foliation of a schistose rock differs markedly 
from the lamination of sedimentary derivative rocks. It 
must also be distinguished from the fluxion or fluidal 
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