BENEFICENT STRUCTURE OF COAL-BASINS. 183 seams, or as floodgates to arrest the diffusion of the subterranean springs. By these natural dams, the water which might inundate the whole, or, at least, entirely submerge the richest deposits of the centre, is confined to a single compartment, from which it, is in most cases practicable to drain it. The eruptive forces, moreover, in creating these mounds to the waters, have, at the same time, upheaved many strata, which, had they been left to follow their natural slope, would have been sunk to inaccessible depths. A coal formation is thus parcelled out into cubical fields, each of which is complete in itself, and to a certain degree independent. But for these slips, the rains which fall profusely on the lofty basset-edges or out-crops of the strata, would percolate down through them, and convert the basin into a subterranean lake, which no human power could possibly drain. Similar eruptive intersections exist in many other strata, and they every where act as cisterns, or even sometimes as pumps, raising in syphon channels a copious supply of spring water to the surface. These safeguards of mines are, therefore, not confined to coal basins, but are providentially distributed through every important mineral bed. In contemplating the effects of any mighty convulsion on his terrestrial abode, man is apt to feel appalled, and to regard the operation as altogether irregular, fortuitous, and uncontrolled, because its magnitude and complexity mock his pigmy conceptions of power. Yet no one will doubt that the primordial erection of the great mountain strata and table lands was the result of wise design, if he study their conformation, and reflect that this earth could not otherwise have become the abode of animation. Nor can we meditate upon the manifold advantages derived from the upheavings of the secondary strata without seeing in them also, traces of Him "who is wonderful in counsel, and excellent in working." The naturalist always contemplates the members of an animal, in reference to its way of life; and can deduce from even a few bones, many of the functions which it performs in this scene of being. For every part he finds a special purpose, nor does he ever dream that the slightest bump or curvature of a bone is made in vain. He seeks the conditions of its existence in the catenation of its frame. Why then is the philosopher to suppose that the framework of the earth itself, should not also have its conditions of existence as definite as those of an inconsiderable bird or insect, nay, incomparably more refined and complex, since it must be in harmonious relation not only with every order of or-. ganic existence, but with the ocean; the atmosphere; heat; light; and the solar system itself? It well becomes us, then, in surveying the various chambers of the terrestrial edifice, if some few apartments should appear in our eyes rudely fashioned, or in disorder, to abstain from all presumptuous judgments, humbly to confess our ignorance, to investigate with diligence and docility, trusting eventually to recognise beauty and wisdom, in what seemed at first sight, deformity and confusion. Final causes which the zoologist must consult at every step, ought not then to be neglected by the geologist. Unfortunately they have been so often abused and CAUSES OF ALTERNATE COAL AND SANDSTONE. 185 misinterpreted by ignorant, though perhaps wellmeaning speculators, that the man of science has become chary of their employment, and pusillanimous in their vindication. But final causes, under inductive restraint, will ever form the noblest and most delightful species of knowledge, comprehending in its sphere, the correlation of the most general physical and moral truths. CHAP. IV-SUPERMEDIAL STRATA. THE appearances of the great coal strata, lead us to believe them formed by alternate earthy and vegetable deposits, in some immense lakes or estuaries of the antediluvian earth. The progress of our inquiries, proves the globe in those times to have been the frequent subject of mighty convulsions, which have disturbed the strata over an extent prodigiously greater than the explosions of modern earthquakes and volcanoes could give us reason to conceive. It is certain that the sea must have participated in the violence under which the solid earth has evidently suffered. Irruptions of the waters over the land, would unquestionably occur at every new crisis of the eruptive power so conspicuous in the coal-measures and basaltic formations. Thus we can understand how the surface of the coal basins came to be covered in several places with a series of sandstones, or of limestone-strata, replete with marine shells.. During all this period also, a series of deposits was forming under the sea, in a determinate order of superposition on its channel. These deposits are characterised by peculiar orders of organic remains. It is known to the naturalist, that shellfish live in colonies; each colony preferring a peculiar ground or locality; and that in general, quartzose sands are shunned by them, as unfavourable to their production. Hence many districts of our ocean-floor are destitute of shells, whilst others are covered with a vast congeries of them. It is ascertained, that if fowls be deprived of access to calcareous matter, they lay eggs unprovided with shells, and eventually lose the faculty of laying them altogether. In like manner, it would seem that there are districts of the sea so deficient in calcareous matter, that molusca cannot there elaborate their calcareous mansions, and consequently shellfish cannot exist. These suggestions will serve to explain many peculiarities observable among the secondary formations. 13 12 11 20 8 5 Over the extensive regions where the coal-measures themselves are absent, the old redsandstone, or the mountain limestone, constitutes, generally speaking, the stratum that represents the place of coal in the geological series, or plane of superposition. On this principle, it is said that the second6 ary rocks are superior to the coal formation, though no coal should really lie immediately below them. Order of Superposition of English Strata, according to Messrs. Conybeare and Phillips. See Fig. on margin. MAGNESIAN LIMESTONE. 187 Great oolite.-5. Cornbrash and Forest marble.-6. Oxford or Clunch clay.-7. Coral rag.-8. Kimmeridge clay; Oak-tree of Smith.-9. Portland limestone.-10. Iron or Hasting's sand.11. Blue marl.-12. Chalk marl with green sand.-13. Lower and upper chalks.-14. Plastic clay and sand.-15. London clay. # The supermedial class of rocks as exhibited in England has been divided into four groups of strata. I. Formations between the coal strata, and lias, including, 1. Magnesian limestone, corresponding in position to the zechstein, the copper-pyritous slate, and rauchwacke of Germany; and to much of the Alpine limestone. It is the first floetz limestone of Werner. Between this series and the coal, there is observed in Germany, a great deposit of red-sandstone and conglomerates, called the red dead-layer (rothe todte liegende), because destitute of the metals found in the beds above it. This is the older or first flætz sandstone of Werner. Much of the sandstone of Southern Africa belongs to this formation. 2. New red-sandstone, or red marl, corresponding to the variegated sandstone of Germany. Rock salt and gypsum occupy this locality. I. MAGNESIAN LIMESTONE. 1. This magnesian limestone is called the newer, to distinguish it from the same mineral associated with the carboniferous limestone. The two differ in their organic remains, and in this upper one containing extensive beds of calcareous conglomerate. The magnesian limestone has a granular sandy structure, a glimmering lustre, and a cream-yellow colour. It often forms large concretional and botryoidal masses; as large as a cannon ball, which are grouped together like chain-shot. It is used for building, and has a pleasing tint. When calcined, it forms a mortar lime. In agriculture it is |