~. Set Raa 
id . 
ORIGIN AND FORMATION OF SOILS. 121 
decomposable rock than granite. It passes through tadcose 
gneiss into 
Talcose Schist, which resembles mica-schist in colors 
and in facility of splitting into slabs, but has a less glis- 
tening luster and a soapy feel. 
Chloritic Schist resembles talcose schist, but has a less 
unctuous feel, and is generally of a dark green color. 
Related to the above are Steatite, or soapstone,—nearly 
pure, granular talc; and Serpentine rock, consisting 
chiefly of serpentine. 
The above are the more common and wide-spread si- 
licious rocks. By the blending together of the different 
members of each series, and the related members of the 
different series, and by the introduction of other minerals 
into their composition, an almost endless variety of si- 
licious rocks has been produced. ‘Turning now to the 
CRYSTALLINE CaLcarreous Rocks, we have 
Granular Limestone, consisting of a nearly pure car- 
bonate of lime, in more or less coarse grains or crystals, 
commonly white or gray in color, and having a glistening 
luster on a freshly broken surface. The finer kinds are 
employed as monumental marble. 
Dolomite has all the appearance of granular limestone, 
but contains a large (variable) amount of carbonate of 
magnesia. 
Tue FRAGMENTAL oR SEDIMENTARY Rocks are as fol- 
lows: 
Conglomerates have resulted from the consolidation of 
rather coarse fragments of any kind of rock. According 
to the nature of the materials composing them, they may 
be granitic, syenitic, calcareous, basaltic, etc., etc. They 
pass into 
Sandstones, which consist of small fragments (sand), 
are generally sidicious in character, and often are nearly 
6 
