“The materials of this crust are not thrown together confusedly; but distinct mineral masses called rock are found to occupy definite spaces and to exhibit a certain order of arrangement. These rocks are divided into four great classes by reference to their different origin, or in other words by reference to the different circumstances and causes by which they have been produced.
“The first two divisions, which will at once be understood as natural, are the aqueous and volcanic, or the products of water and those of igneous action at or near the surface.… The aqueous rocks, sometimes called sedimentary or fossiliferous, cover a larger part of the earth’s surface than any other. These rocks are stratified, or divided into distinct layers or strata; these strata have been generally spread out by the action of water, like what we daily see taking place near the mouth of rivers or on the land during a temporary inundation.
“The remains of animals, especially of aquatic species, are found almost everywhere, imbedded in stratified rocks; and sometimes, in the case of limestone, they are in such abundance as to constitute the entire mass of rock itself. Shells and corals are the most frequent, and with them are often associated the bones and teeth of fishes, fragments of wood, impressions of leaves, and other organic substances.
“When geology was first cultivated, it was a general belief that those marine shells and other fossils were the effects and proofs of the deluge of Noah; but all those who have carefully investigated the phenomena have rejected this doctrine. A transient flood might be supposed to leave behind it, here and there upon the surface, scattered heaps of mud and sand and shingle, with shells confusedly intermixed; but the strata containing fossils are not superficial deposits, and do not simply cover the earth, but constitute the entire mass of mountains. Ample proof of these reiterated revelations is given, and it will be seen that many distinct sets of sedimentary strata, each several hundreds or thousands of feet thick, are piled one upon the other in the earth’s crust, each containing peculiar fossil animals and plants, which are distinguishable, with few exceptions, from species now living. The mass of some of these strata consists almost entirely of corals, others are made up of shells, others of plants turned into coal, while some are without fossil.
“Volcanic rocks are those which have been produced at or near the surface, whether in ancient or modern times, not by water, but by the action of fire or subterranean heat. These rocks are for the most part unstratified, and are devoid of fossils.
“There are two other divisions of rock, called Plutonic rocks, granite, etc., and Metamorphic, or stratified crystalline rocks. The members of both these divisions of rocks agree in being highly crystalline and destitute of organic remains.
“The composition of the aqueous rocks, mineral composition of strata: These may be said to belong principally to three divisions, as follows:
“1. Arenaceous or siliceous rocks. Beds of loose sand frequently met with, of which the grains consist entirely of silex, which term comprehends all purely siliceous minerals, as quartz and common flint. Quartz is silex in its purest form; flint usually contains some admixture of alumina and the oxide of iron. Silica is the mineral used in the manufacture of glass, mixed with a little potassium oxide and lime, or lead, etc.
“2. Argillaceous rock. A mixture of silex or flint with a large proportion, usually about one-fourth, of alumina or argil; but in common language, any earth which possesses sufficient ductility, when kneaded up with water, to be fashioned like paste by the hand or by the potter’s lathe, is called clay. Such clays vary greatly in their composition. They are, in general, nothing more than mud derived from the decomposition or wearing down of various rocks. The purest clay in nature is porcelain clay or kaolin, which results from the decomposition of a rock composed of feldspar and quartz, and it is almost always mixed with quartz. (The kaolin of China consists of 71.15 parts of silex, 15.86 of alumina, 1.92 of lime, and 6.73 of water.)… One general character of all argillaceous rocks is to give out a peculiar, earthy odor when breathed upon, which is a test of the presence of alumina.
“3. Calcareous Rocks. These consist mainly of chalk—lime and carbonic acid. Shells and corals also are formed of the same elements, with the addition of animal matter. Any limestone which is sufficiently hard to take a fine polish is called marble. Many of these are fossiliferous; but statuary marble, which is also called saccharine limestone, as having a texture resembling that of loaf-sugar, is devoid of fossil. Siliceous limestone is an intimate mixture of carbonate of lime and flint, and is harder in proportion as the flinty matter predominates. Marl slate bears the same relation to marl which shale bears to clay, being calcareous shale. Magnesian limestone is composed of carbonate of lime and carbonate of magnesia; the proportion of the latter amounting in some cases to nearly one-half. It effervesces much more slowly and feebly with acid than common limestone. Gypsum is a rock composed of sulphuric acid, lime, and water. It is usually a soft whitish-yellow rock, with a texture resembling loaf-sugar, but sometimes it is entirely composed of lenticular crystals. Alabaster is a granular and compact variety of gypsum found in masses large enough to be used in sculpture and architecture. It is sometimes a pure snow-white substance. It is a softer stone than marble and more easily wrought.”