1

ceding, with respect to its ingredients. It is generally of a greenish ground, marked with white yellow, brown, or reddish spots, so as to bear some resemblance to the skin of a snake. From this circumstance it derives its name. Rocks and hills of this substance are found in Siberia; near the White Sea; in Germany; on the coast of Cornwall; and in the vicinity of Genoa.

11. Porphyry. This stone generally consists of the same materials as granite, but in different proportions, and of a very different appearance. It is found in the greatest abundance in tropical countries.

12. Pudding stone and Breccia. These are stones composed of fragments of other stones, cemented by hardened clay, and are found in many parts of the world in great abundance.

13. Syenite. A greenish, granulated substance, deriving its name from Syene, in Upper Egypt, where it was raised in great quantities, and sent to Rome for public edifices.

14. Primitive Limestone. This stone is of a granular structure, and of a whitish grey colour, though sometimes of a dark iron grey, or of a reddish brown. There is in Spain an extraordinary mountain of this substance, named Filabres. It is white; three miles in circumference, and two thousand feet high, without any mixture of other earths or stones, and having scarcely any fissure.

15. Primitive Trap. Trap is a name given by Swedish mineralogists, to distinguish certain stones which are of a compact texture, and a

dark colour, composing part of several mountains. But many rocks have received the common name of trap.

Primitive trap frequently contains metals, and is found in vast strata, in the midst of gneiss, granite, and micaceous schist. Fifteen other substances are enumerated by geologists; the most important of which are gypsum, or plasterstone. Of this there are six varieties.

Chalk. This substance, so well known, is not always white, but is frequently found coloured. It is disposed in horizontal beds, often many yards thick, and which always repose on layers of other calcareous stones of harder structure.

Clay.

This substance is found in various states with respect to hardness or solidity, from the soft ductile clay of the potter and pipe maker to the perfect slate.

Marl. A substance chiefly composed of sand, clay, and calcareous matter, which is found in many places, and forms one of the most valuable natural manures used in agriculture.

Rock Salt. This is the purest salt found in nature, being less impregnated with extraneous matters than what is procured from sea-water. It is hard; commonly transparent; generally white; but sometimes yellow, blue, red, or violet. This salt forms horizontal beds or banks, of immense extent, and often very deep in the earth.

Coal. This substance, which is of such vast utility to man, is commonly solid, black, very dry, and considerably hard, and combustible, existing in various forms and species. It has been used for fuel in this country, for many

centuries. Coal lies in strata or beds, like other mineral substances, frequently of very great extent, and in various directions. The beds in which coal is disposed, usually have their extremities near the surface of the ground, from which they bend obliquely downwards, the middle part of the bed being nearly horizontal. Coal, in a greater or less quantity, has been found in most countries, and probably exists in all.

Those organic remains of vegetable and animal matter which are found below the surface of the earth, mixed with those stony matters which are properly the component parts of the earth, are generally called fossils, or extraneous fossils. If they have entirely lost all traces of animal or vegetable matter, and have assumed a stony, earthy nature,they are then styled petrifactions. Almost every part of vegetables, and even whole trees, are found in a fossil state, below the surface of the earth, particularly in bogs and mosses. These, sometimes, retain much of their vegetable nature, but are more commonly impregnated with bitumen, or completely petrified. Fossils of animal matters, are still more common than those of vegetables. Shells and bones are found in almost every bed of limestone, and in all countries, at the bottom of the deepest valleys, and on the summits of many high mountains. Entire skeletons of very large

animals have been discovered in a fossil state. In the plains of Siberia, have been found, buried at different depths, skeletons of elephants, and bones of the hippopotamus, and of still larger animals, whose species are supposed to have been long extinct.

QUESTIONS.

What is geology, and into what branches is this science divided? How are the materials of which the general mass of the earth is composed, distributed? How are these materials classed by modern geologists? What are the principal primitive substances? What are fossils and petrifactions? What are vegetable fossils ? What are animal fossils?.

CHAP. XXXII.

THEORIES OF THE EARTH.

THE theories which now divide scientific men are those of Hutton and of Werner.

THEORY OF HUTTON. -The leading principles of the Huttonian theory, are, first, that the greater part of the bodies which compose the exterior crust of our globe, bear the marks of being formed of the materials of mineral and organized bodies, the spoils or wrecks of an older world. Secondly, that the present rocks, excepting such as are not stratified, have all existed in the form of loose materials at the bottom of the sea, and must have been consolidated and converted into stone, by virtue of some powerful and general agent; which agent is subterraneous heat. Thirdly, that the stratified rocks have been raised by the action of some expansive force placed under them. This force, which has burst in pieces the solid pavement on which the ocean rests, and has raised up rocks from the bottom of the sea, into mountains fifteen thousand feet above its surface, is supposed to

be heat. Fourthly, that this force, heat, melted those mineral substances which are found injected into the chasms existing in the various strata of materials, of which the earth's body is composed. Fifthly, this theory states, that all the mineral bodies thus raised into the atmosphere, are going to decay; that from the shore of the sea, to the summit of the mountain, from the softest clay, to the hardest quartz, all are wasting and undergoing a separation of their parts. The bodies thus resolved into their elements, whether chemical, or mechanical, are carried down, by the rivers, to the sea, and are there deposited.

THE THEORY OF WERNER. The Wernerian theory assumes, that the exterior part of the globe has been entirely dissolved by the waters which surrounded it; and that from this solution, certain chemical precipitations took place, which have formed that crust, or surface of the earth,

which we now see. It supposes that these chemical precipitates did not form a regular surface, but that they collected here and there, so as to form the primitive mountains; that after the retreat of the waters, these elevated parts were first discovered; that being exposed to the destructive action of the elements, and the shock of tides and torrents, the valleys were hollowed out, and the mountains acquired nearly the form in which we now see them.

Werner imagines six of these precipitations or formations to have taken place; four of which he names universal formations, their products being found over the whole globe; the other two,