> >? eee ae 
rn ale 
118 HOW CROPS FEED. 
clay into granite. These rocks, which are the result of 
the united action of heat and water, are termed meta- 
morphic (i. e., metamorphosed) rocks. 
One of the most obvious division of rocks is into Crys- 
talline and Fragmental. 
Crystalline Rocks are those whose constituents crystal- 
lized at the time the rock was formed. Here belong both 
the igneous and metamorphic rocks. These are often - 
plainly crystalline to the eye, i. e., are composed of readily 
perceptible crystals or crystalline grains, like statuary 
marble or granite; but they are also frequently made up 
of crystals so minute, that the latter are only to be recog- 
nized by tracing them into their coarser varieties (basalt 
and trap.) 
Fragmenta! Rocks are the sedimentary rocks, formed 
by the cementing of the fragments of other older rocks 
existing as mud, sand, ete. 
THE CrystTaLttInE Rocks may be divided into two 
great classes, viz., the silicious and calcareous ; the first 
class containing silica, the latter, lime, as the predomina- 
ting ingredient. 
The silicious rocks fall into three parallel series, which 
have close relations to each other. 1. The Granitic series ; 
2, The Syenitic series; 3. The Zalcose or Magnesian 
series. In all the silicious rocks quartz or feldspar is.4 
prominent ingredient, and in most cases these two minerals _ 
are associated together. To the above are added, in the 
granitic series, mica ; in the syenitic series, amphibole or 
pyroxene ; and in the talcose series, tale, chlorite, or ser- 
pentine. The proportions of these minerals vary indef- 
initely. 
Tue Granitic SERIES 
consisting principally of Quartz, Feldspar, and Mica. 
Granite.— A hard, massive* rock, either finely or 
+ Rocks are massive when they have no tendency to split into slabs or plates 
