112 _  GEOGNOSY AND GEOLOGY. 
Calcareous Soil. An excess of calcareous particles in loose mixture 
with clayey and sandy matters. It is of a light color, often changed by 
humose substances. It absorbs water, yet without becoming plastic, and 
readily parts with it again. It overlies chalk, calcareous tufa, and other 
limestone rocks. 
Tron-clay Soil. This is of a reddish-brown color, and arises from 
disintegrated iron-clay or decomposed ferruginous rocks. It readily takes 
up water, and holds it very tenaciously. On the escape of the water the 
earth shrinks and becomes fissured. 
Tron Soil. This is of very complex composition, and appears to be 
principally a product of decomposition of pyroxene and amphibolie rocks. 
The considerable proportion of oxyde of iron imparts to it a yellowish or 
brown color. It absorbs much water, retains it firmly, and parts with it 
again without fissuring. 
Humose Soils. The humus which characterizes this soil rarely amounts 
to over one fourth of the entire mass. Sand, clay, and more rarely lime, 
are associates in it. When dry it is very apt to be dusty, and when wet 
of a boggy or miry character; its color is brown or brownish-black. — It 
readily combines with water, and contracts slightly on drying. Many kinds 
of humose soil are known in agriculture. Among these the heath soils are 
conspicuous: soils with remarkable hard particles, resulting from the , 
decomposition of species of erica or heath. 
It frequently happens that fragments and blocks of various rocks are 
distributed in soils, of various shapes and sizes, and in such excess as almost 
to displace the soil itself. The manner and origin of their accumulation, as 
well as the petrographical peculiarity of these fragments, are entirely 
dependent on the position of the bed of the earth. The most conspicuous 
ingredients occurring here and there in soils are gold, arsenical pyrites, and 
iron pyrites. The ground is frequently impregnated with various salts, 
which, under favorable circumstances, eflloresce so as to form a white 
incrustation. The principal of these salts are common salt, glauber salts, 
epsom salts, potash and soda, saltpetre, We. 
Series 3. Sands. 
These embrace masses presenting themselves as accumulations of fine 
angular or rounded grains. They are generally quartzose, although 
other substances than quartz may constitute sand. The principal species 
are : 
Quartz Sand, or a loose accumulation of quartzose particles. There are 
various modifications, characterized by a greater or less degree of purity. 
Yellow sand derives its color from hydrated oxyde of iron, this being so 
firmly combined as to require the action of acids to eradicate it. The 
principal varieties of sand are characterized by the presence of lime, 
dolomite, augite, garnet, iron, mica, gold, platinum, shells, &c. Jewel 
sand contains many of the precious stones, as diamond, spinelle, zircon, 
garnet, &c. 
Series 4. The Gravels. 
Here belong those very loose aggregates which plainly exhibit traces of a 
542 
