16 OF THE EARTH AS A MASS. 
tute a part of the mass of the earth. But if the interior agree in its 
composition with the exterior crust, no more than twelve are there 
in any considerable quantity, the others being of rare occurrence, 
and entering sparingly into the composition of rocks of moderate 
magnitude, in the localities where they are found. 
The twelve more abundant constituents of the earth's crust are 
Oxygen, Silicon, Aluminum, Calcium, Magnesium — Hydrogen, 
Carbon, Sulphur, Chlorine, Potassium, Sodium and Iron, of 
which the first five are more common, and enter more largely 
than the others into the composition of the rocks. These are 
arranged in what is supposed to be the order of their abundance. 
It is difficult to determine in regard to the remaining seven, what 
are their relative quantities. These elements form by their union 
about eleven binary compounds, (oxides and acids with a single ex- 
ception) which are the proximate elements of the simple minerals ; 
as these minerals are of the rocks that form the crust of the globe. 
The minerals that constitute 99 one hundredths of the rocks, and 
that have produced by their decomposition the soil of all coun- 
tries, are not more than twelve in number, viz : 
1. Indurated Clay, 5. Hornblende, 9. Serpentine, 
2. Quartz, 6. Tal§, 10. Carbonate of Lime, 
3. Feldspar, 7. Steatite, 11. Sulphate of Lime, 
4. Mica, 8. Chlorite, 12. Iron and its oxides. 
These minerals will be further noticed in the order in which 
they have been mentioned, and a few of their distinctive char- 
acters briefly stated. 
1. Indurated Clay. — Of this substance the common writing 
and roofing slates, and many of the slate rocks that underlie the 
central counties of North Carolina, may be cited as examples. 
In these it exhibits a schistose structure, so as to be readily divisi- 
ble into thin laminae, and forms a simple rock by itself; but it 
is often massive and associated with other minerals. 
2. Quartz, is a mineral with which every person is familiar 
under the name of white flint. It often occurs in considerable 
masses, and under the form of small grains enters into the com- 
position of many of the rocks, forming sand when they are dis- 
integrated. The soil cf the low country of North Carolina, is 
mostly a mixture of quartzose sand and clay. Fused with an alkali 
and lime, or oxide of lead, it forms glass. 
3. Feldspar, is easily recognised when we are once acquainted 
with it, but is not as readily distinguished as some of the others, 
by a person ignorant of mineralogy, who has only a description 
to guide him. It has not the glassy lustre of quartz, is less hard, 
has a laminated structure, is commonly either white or flesh 
colored. It exists under the form of coarse angular grains, in 
immense quantities, in the northern and western or granitic coun- 
ties of North Carolina, of which, along with quartz, it constitutes 
almost the whole soil. 
