58

SECTION VI.

CHANGE OF TEMPERATURE.

ASSUMING for a moment the truth of a very prevalent opinion, that the temperature of the globe was at one time very high, and that it has gone on progressively cooling to its present rate, we may remark, that even this theory refutes the idea of a long succession of ages being necessary for the formation of the respective strata.

We shall take for example the coal measures,-a mass of alternating strata, from three to five thousand feet thick in its deepest parts, and requiring, according to the liberal allowances of some, not less than a million of years for its formation. Now, the vegetable remains at the bottom of this series are identically the same as those at the top; but had a refrigération of a million of years taken place in the interval, the last lepidodendron and fern should have had a totally different character from the first. The same remark applies to beds of molluscous animals.

But, indeed, we can never consider the common theories of central heat as compatible with the existence of plants or animals in a considerable portion of the globe, at any period of its past or present existence. Thus, all will allow that our present tropical temperature is due to the sun's influence alone, and the average of this heat for several months is upwards of one hundred degrees of Fahrenheit. Now, to this average heat, which must have been produced ever since the sun shone upon the earth, add fifty or sixty degrees of central heat, and we have a climate that might boil plants and animals, but would never permit them to exist.* And yet we have the carboniferous coal fields of India with the same fossils, and coeval, it is said, with the same systems of Britain! The temperature of the former and present surface of the earth, different as it seems to have been, must, we suspect, be explained on other data than theories of central heat, and none seem more fitted for this purpose than the relative change of position of large portions of land and sea, as illustrated in so ingenious a manner by Mr Lyell.+

* The mean tropical heat is calculated at 81 degrees.

At Cawnpore, E. I. in April and May, 1789, the mean heat was 127 degrees, maximum 144 degrees.

At Allahabad, E. I. the heat is often 109 degrees in the shade.

In Georgia, maximum of heat 105 degrees.

A heat of 109 degrees proved fatal to ten thousand persons in

China.

† Note VI.

Allowing the probability of this latter theory, the following considerations seem accordant to facts,—

The change was sudden and abrupt. In Europe we have no traces of intermediate vegetation between the system of extinct plants and existing species. We have animals of tropical temperatures supplanted by our present races, and some of the former, as the Siberian elephant, suddenly enveloped in clay, and frozen over so as to be completely preserved.

The change was extensive, because the coincidence of the same plants, as in the carboniferous system, and the same animals, as in fossil beds and diluvium, extending over many regions of the globe, exhibiting one era of existence, all indicate a similarity of climate. This temperature, though more elevated and uniform than that of our temperate and frigid zones, may not, however, have been even equal to our present tropical. We cannot determine, in fact, how slight or how great an elevation of temperature may have been necessary for the growth of fossil plants, or the existence of fossil animals. Thus, the Siberian elephant was clothed with long hair, indicative of a temperature not extremely warm, probably analogous to many mountainous regions in Asia, where hairy elephants were seen by Bishop Heber.

61

SECTION VII.

OPERATIONS AT PRESENT IN PROGRESS.

It is, we believe, almost generally allowed, that the commencement of the present system of things on the earth's surface does not claim a very remote antiquity that, according to one view of the question, it cannot have a date anterior to the period of man's creation as fixed by Moses, or, according to others, an earlier commencement than the epoch of the Noachian deluge. A third party, it is true, are more indefinite in their chronology, but still fix the period of the introduction of man on the earth, and the commencement of the existing epoch, within the compass of the last six thousand years.*

It remains to be considered, then, whether there are any indications on the earth's surface to furnish data for such conjectures, and how far these are to be depended upon.

* Note VII,

The mechanical forces continually at work in the inorganic world are daily and yearly making inroads on the solid matter of the globe, and these, again, are aided by the chemical operations called into action by the multitudes of organized existences. The combined operations of these, then, must, in a long series of ages, have left obvious traces of their effects on the earth's surface; but we must call to mind that, from the very nature of these forces, the effects must be far more extensive and conspicuous in the bed of the ocean than on dry land.

Accordingly, when we strictly investigate the operations of time on the surface of the earth, we cannot help feeling a degree of astonishment at the little change which the lapse of three or four thousand years has brought about. Except in particular localities, we neither see a great extent of waste, nor a great accumulation; we see a partial mouldering down of rocks and precipices, and a slow excavation of valleys; a gradual disappearance of headlands, and a filling up of flat shores and shallow marshes; but the great features of continents and islands still remain unchanged-the same mountains on which the sages of antiquity looked, still rear their venerable summits-the same fields and meadows stretch out their ever verdant surfaces the same streams and mighty rivers flow continually down from their mountain sources. To counteract the destructive powers of nature, there are compensating operations