greater than air by weight, so that five gallons of water in cooling only one degree F. can warm by the same quantity 2650 cubic feet of air, being the contents of a chamber about 16 feet square and 10 feet high; we see what a genial climate would be created over the earth from pole to pole, under such an order of things. Then the intrinsic source of terrestrial heat, having its diffusive energy but slightly obstructed, would be paramount over the solar; so that the position of the sun, relative to the equator, would act a very subordinate part in modifying climate, instead of being its sovereign arbiter, as at the present day. Plants which love a warm but humid atmosphere, like the equisetums, ferns, &c. would multiply and flourish under such circumstances with nearly equal vigour in the Arctic Regions, as under the Line. Hence also the difference of equatorial and polar temperatures would be at first comparatively small, so that a considerable uniformity of vegetation would pervade the most distant zones. We need not, therefore, be surprised at finding the same Calamites or gigantic equisetums buried among the coal-measures of New Holland (near Port Jackson), and of England; though nowadays, that plants are subjugated to the undivided empire of the sun, they differ in species with very moderate variations of latitude; and with every change of hemisphere.

The first age of the world then, extending probably through several centuries, fully realized the universal and unfading spring of the poets. Under such fostering powers of vegetation, the coal-measure plants were matured, in countless myriads,

SECONDARY STRATA CONSIST OF TRIADS. 431

with a rapidity to which modern experience can furnish no parallel. But the tremendous catastrophes of the crust of the earth, that took place soon after this period, of which the dislocations and disruptions of the coal-strata themselves exhibit magnificent memorials, generated a vast quantity of detritus from the older rocks, which at first diffused through a turbid ocean, progressively subsided on its bottom in the chemical order of deposition; constituting beds of conglomerate limestone, red marl, and lias; in variable proportions of thickness and extent according to the nature of the exploded and comminuted rocks. In the secondary formations of Geology, in fact, we see nothing but a repetition of mineral triads; shells more or less fractured, covered with a twofold coat, the undermost of sand or sandstone, the uppermost of clay more or less indurated. The tepid ocean-bed vied in fecundity with the glowing soil round its shores, and thus was covered with a thick deposit of shellfish and their exuviæ. At each rencounter of the water and subjacent explosive metals, these shells would be more or less scattered and broken down, and when tranquillity returned, covered with their siliceous and argillaceous mantles.

The conglomerate limestone, and red marl, are referred by geologists (see Conybeare and Phillips) to the detritus of the primitive and transition rocks; deposits just posterior to the coal formation. It is probable that the submarine disturbances of that particular age were unfavourable to the multiplication of mollusca. But a period of repose seems to have followed in which the shells

of the lias were elaborated. These, with a little alumina, are condensed into the lithographic stone, and buried under a loamy compound of sand and clay. We have next the inferior oolite; merely a congeries of pulverised shells; roofed with the cornbrash, &c., and overlaid with the Oxford clay. Then we come to the Coral Rag teeming with vestiges of vitality; inhumed also beneath its sheet of Kimmeridge clay.

When we arrive at the Portland strata, we must consider that a series of most imperfect conductors of caloric, fully half a mile in thickness, had been by this time interposed between the bottom waters of the sea, and the deeper primitive or transition crust, on which they originally reposed.*

* The aggregate thickness of the supermedial and superior mineral strata of England, may be safely estimated at about a mile. The following table is compiled from authentic documents.

CRISES OF ANTEDILUVIAN CLIMATES.

433

The climate of the earth should therefore indicate about the Portland era, an abatement of the hypertropical temperature of the first age. "The cycadenoidea" (fossil plants akin to the cycas family of Malabar, &c.) "says the Rev. Dr. Buckland, render it probable that the climate of these regions, at the time when the oolites were deposited, was of the same warm temperature with that which produces a large proportion of the existing cycadeæ. M. Adolphe Brogniart is also of opinion that it exceeded the temperature of our modern tropics at a still more early period, when it maintained the extraordinary vegetation of the great coal formation; and that it was less than tropical, though warmer than it is at present, in the period to which we owe our tertiary strata. To this theory I see much reason to incline, and confidently look forward to its future development in the examination of the Flora of the fossil world, which he is now so actively conducting."*

Our principles lead irresistibly to the same conclusion, for posterior to the Portland epocha, successive submarine catastrophes of greater or less extent, caused those successive disturbances of the waters, from which the superjacent beds of the iron sand, Weald clay, &c., were deposited up to the

I am well aware that each of the preceding beds does not always lie with all its mass directly above those which precede it in the list; but that they thin off, and wear out in various directions; yet still the average thickness remains substantially correct, in consequence of mutual compensations among the different strata. The argument in the text depends on no such minutiæ of measurement.-See Conybeare and Phillips passim.

* Geol. Trans. 2d Series, 2d vol. p. 400.

tertiary formations; the freshwater portions of which were evidently connected with the copious emission of hot springs. The temperature of the surface in these high latitudes of ours, was still genial, though reduced by the progressive operation of the causes already named, and others to be presently described. Finally the great turmoil of the Noachian deluge, placed the terraqueous equili brium on a more stable basis; introducing at the same time a lower but more regular and settled scale of temperature.

We have hitherto confined our views to the progressive interception of the subjacent heat from the ocean, and thereby from the surface of the earth in proportion as the secondary deposits were thickened after each convulsive catastrophe. But other considerations must now be introduced. While the series of deposits, impervious to water, were consolidating in alternate beds, and separating the ocean, further and further from the primordial envelope of the interior fires, a great mechanical change was simultaneously taking place on the terraqueous constitution, whose influence in refrigerating climate merits deliberate research. We cannot however consider this change as uniform in its march; but as advancing by successive catastrophes at distant intervals. It is of the nature of volcanic action to intermit and return in temporary crises. Such periods of violence and repose, cor

See pages 202, 252, 263, 265, 270, &c., for notices of the retentive strata in England, which intercept the percolating waters, and throw out the springs at successive levels.

+ Volcanoes do not lance out perpetual fires, nor do lavas always