The coal beds contain many impressions of plants and portions of plants, so that geologists have been able to determine the nature of the vegetation of that period. There are a great many mosses and ferns, some of the latter having thick, broad stems, and long and heavy leaves. One geologist says there are one hundred and seventy-seven specimens of plants found in single coal beds. He says there are no palms, nor grasses, nor flowering plants; and for this reason he considers that the coal beds were formed from plants of a marshy growth. The layers of peat, after being covered by shales, sandstone, and limestone, were compressed beneath the enormous weight of the over-lying strata, and while undergoing this compression, there was a sort of distillation and purifying process going on. In this way the plants and peat, originally loosely matted together, became more and more compressed, and by means of the heat and pressure were entirely decomposed. Ultimately the substance was turned into what we now find it, and the coal was stored up for future ages. The ancients had curious theories in regard to the formation of coal. They regarded it as streams of bitumen, which had become petrified, or had impregnated certain very porous kinds of rock. Another theory which they entertained was, that forests had been carbonized on the spot where they grew, or had been transformed by streams of sulphurous acid, which possesses the property of hardening and carbonizing wood. It is easy to attribute the origin of coal to the agency of rivers of bitumen, and oil of vitriol; but it is not easy to say where those rivers came from. [Sidenote: SACRED FIRE WELLS.] The Chinese have a theory that coal is a species of plant of which the seed was deposited in the earth ages and ages ago, and that it grew and spread in different parts of the empire where it is now found, in order that the Chinese of to-day might have a sufficient supply of fuel. They attribute the streams of inflammable gas, which they collect and utilize, to the breathings of an immense monster below the surface of the earth, and in some localities they call him the first cousin of the God of Fire. The God of Fire is one of the Chinese deities. He occupies a prominent place in the temples, and is worshipped with great solemnity. In other parts of the world these streams of gas are worshipped, and in localities along the coast of the Caspian Sea, streams of burning gas are constantly rising, and their sources are known as sacred wells. They are visited by thousands of devotees every year, and are regarded with the greatest reverence.