There is however great difficulty in accounting for the universal stratification of the solid globe of the earth in this manner, since many of the materials, which appear in strata, could not have been suspended in water; as the nodules of flint in chalk-beds, the extensive beds of shells, and lastly the strata of coal, clay, sand, and iron-ore, which in most coal-countries lie from five to seven times alternately stratified over each other, and none of them are soluble in water. Add to this if a solution of them or a mixture of them in water could be supposed, the cause of that solution must cease before a precipitation could commence. 1. The great masses of lava, under the various names of granite, porphyry, toadstone, moor-stone, rag, and slate, which constitute the old world, may have acquired the stratification, which some of them appear to possess, by their having been formed by successive eruptions of a fluid mass, which at different periods of antient time arose from volcanic shafts and covered each other, the surface of the interior mass of lava would cool and become solid before the superincumbent stratum was poured over it; to the same cause may be ascribed their different compositions and textures, which are scarcely the same in any two parts of the world. 2. The stratifications of the great masses of limestone, which were produced from sea-shells, seem to have been formed by the different times at which the innumerable shells were produced and deposited. A colony of echini, or madrepores, or cornua ammonis, lived and perished in one period of time; in another a new colony of either similar or different shells lived and died over the former ones, producing a stratum of more recent shell over a stratum of others which had began to petrify or to become marble; and thus from unknown depths to what are now the summits of mountains the limestone is disposed in strata of varying solidity and colour. These have afterwards undergone variety of changes by their solution and deposition from the water in which they were immersed, or from having been exposed to great heat under great pressure, according to the ingenious theory of Dr. Hutton. Edinb. Transact. Vol. I. See Note XVI. 3. In most of the coal-countries of this island there are from five to seven beds of coal stratified with an equal number of beds, though of much greater thickness, of clay and sandstone, and occasionally of iron- ores. In what manner to account for the stratification of these materials seems to be a problem of greater difficulty. Philosophers have generally supposed that they have been arranged by the currents of the sea; but considering their insolubility in water, and their almost similar specific gravity, an accumulation of them in such distinct beds from this cause is altogether inconceiveable, though some coal-countries bear marks of having been at some time immersed beneath the waves and raised again by subterranean fires.