By a reference to the present condition of the ocean, too, some light may be thrown on the mode of formation of the ancient strata.

Thus, the upper portions of the ocean are much agitated by currents and winds, while the lower portions remain comparatively calm and undisturbed. Gneiss, and the so-called primary schists, have evidently been deposited at great depths where the water was still; hence their regular lamination of structure, the minute and uniform comminution of their particles, and the still and placid manner in which these particles have been deposited.

The transition series again marks a period of commotion and turbulence, of rocks violently broken up into fragments, and of water-worn pebbles, transported by currents, and accumulated in frequent layers of <varied conglomerates. The same observations will apply to the older sandstones, while the calcareous mud of the lias points out the action of currents, carrying the lighter detritus of rivers a considerable way into the deeper sea. The oolites, again, are still more littoral; and being formed nearer the genial surface of the water, afford a suitable bed for those numerous species of melanie or infusory tribes, of which the spherical portions of this rock are, according to Ehrenberg, supposed to be chiefly composed, and which impart to it its peculiar character.

The mountain limestone-beds were most probably reefs of corals and encrinites rising nearly to the surface, but constituting a locality different in temperature and other respects, from the more littoral oolite. Over these reefs, probably after they have suffered depression, or some other change, the coal-measures appear to have been deposited. These carboniferous beds, extending in thickness from 2000 to 3000 feet, appear to be an exception to the other marine strata in this respect, that there is a uniformity of fossils throughout, the same organic remains appearing in the lower beds as in the upper. This is to be accounted for from the circumstance that the fossils are almost all vegetables which have grown on the earth's surface, and must have been successively transported into their position by fluviatile currents from the land; or, that part, if not the whole, may have successively grown on the surface of the same locality on which they are now found, and that this surface has repeatedly been submerged by the gradual or periodical sinking of the strata below. A few fluviatile shells and fishes are occasionally interspersed, as also layers of marine lime-stone, with fossils; but the different species do not assume that successive position which the true marine-beds uniformly do, even in strata of the thickness of a few hundred fathoms. This exception of the coal strata to the general law appears to afford an interesting test of the mode of arrangement which is universally prevalent in all the other series. The presence or absence of any one of the series of geological formations may also be readily accounted for from the depth or shallowness of the ancient ocean on any given locality. Thus, the prevalence of the oolitic

and tertiary formations in the region of the Alps, and, indeed, in the whole centre of the continent of Europe, implies a shallow state of the ancient seas there. The same appears to have been the case in the south of England, while the sea would appear to have gradually deepened to the north-west of England, and continued deepening onwards throughout Scotland. In South America, according to Elie de Beaumont, there is an entire absence of the oolitic series, while the gneiss, schistose, and silurian systems are extensively diffused. The chalk and tertiary strata are also extensive, thus shewing a sea with deep and shallow bottoms, but a deficiency of a middle level. It frequently occurs that some of the higher formations, as the chalk or oolite, repose directly upon gneiss or schistose strata; this may arise from an elevation of these deeper beds at once to the natural level of the higher strata, without affording an opportunity for the formation of intermediate beds, or, rather, a fit locality for the peculiar animals which inhabit such.

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When any of the strata are thus raised above their appropriate levels, may be supposed that their inhabitants, or those of them that have escaped destruction, immediately retire to lower levels.

It is a circumstance frequently remarked by geologists, that fossil remains, especially of fishes, are found only at particular points, as, for instance, in a seam of shale of a few inches thick, while above this shale many hundred feet of the same strata may exist without a trace of any organism. This may indicate a convulsion of the oceanic bottom by which myriads of fishes were entombed at once; while, at the same time, the stratum was depressed far below its proper level, by which means the detritus afterwards deposited was at too great a depth to be tenanted by living beings. Or the super-imposed detritus may have been suðdenly drifted and accumulated over the shale, without any great change of level. This drifting by currents or convulsions of the ocean appears to have been the cause of many of the vast accumulations of marine sandstones which are not unfrequently visible; and which, for many hundred feet in depth, exhibit few or no traces of organised bodies; and even such as are found, consist only of the detached scales or bones of fishes, as if the bodies to which they had belonged had been broken up and destroyed by the violent action of the waters.

Although depressions of strata may occasionally take place, yet it is evident that such are of much less frequent occurrence than elevations, because we very rarely, indeed, meet with a reversal of the order of position which the labours of modern geologists have so successfully established as generally, we may say almost universally, existing. Indeed, it is astonishing to find with what accuracy fossil remains preserve their respective positions in the earth's strata in every region of the globe which has yet been explored by the geologist. Thus, the equivalents of the British strata, containing almost identically the same fossils, have been found on the continent of Europe, in Asia, in America, in the re

motest lands of the Pacific Ocean; nay, even in the now frigid climates of the Arctic and Antarctic circles.

This uniformity of its inhabitants would seem to indicate a uniformity of temperature, and other conditions of the primeval ocean, differing from those which prevail in the present seas, and a difference in distribution of animal life over the various regions of the earth.

We shall not here enter into the changes which marine animals, and especially testaceous molluscs, undergo, in consequence of differences of locality, temperature, and other external circumstances, because this is a subject which belongs more properly to considerations regarding the past and present temperature of the general surface of the globe. It may be remarked, however, that such external circumstances give rise to changes, in many cases amounting even to specific differences, in the appearance of the animals. Thus, the testaceous inhabitants of inland seas and gulphs are pigmies compared to their congeners of the open ocean ;* and not only size, but colour, and even form of shell, may be changed. In those raised beaches which are so common in Scotland, and on many of the coasts of the European continent, testacea are found apparently with specific differences from those existing in the contiguous seas. Thus, on the banks of the Clyde, species have been found having more of an arctic character than those of the same family at present existing in that estuary. Now, this may have arisen simply from a change of level in the locality, altering, in some slight degree, the temperature, such as a rise of the channel of the Frith, and a consequent shallowing of the water. In this way, the depth of the waters of the Clyde may have been formerly such as to permit of localities more approaching in temperature to that of the friths of arctic regions.

If the above conclusions are found to be based on sound deductions, our geological systems will, at least, require somewhat of revisal.

In the first place, the mineralogical character of rocks will be that on which their proper arrangement and classification must depend. Thus, if calcareous mud, brought down by currents, is deposited at a certain depth in the ocean, it becomes tenanted by producti and ganoid fishes. The same mud, if deposited at a higher level, is taken possession of by belemnites and ammonites; in the one case, it is called carboniferous limestone, in the other lias.

The present nomenclature, too, of primary, secondary, and tertiary, an, in many cases, only convey erroneous impressions. The same may said of many other terms pointing out a precedency of formation or elative age.

Organic remains will henceforth indicate the respective, and, perhaps, y analogy with living species, the actual depth at which the strata in hich they are contained were situated in the primeval ocean. They are

*E. Forbes, Esq.

James Smith, Esq., Jordanhall, Edin. Phil. Journal.

not the true tests of the relative ages of strata; nor has the Trilobite, inhabiting the profound depths of the ocean, any title to priority of birthright over the humble Cardium, which burrows among the superficial sands that lie barely within tide-mark. Strata of high and low levels, may be found in immediate contact, without the aid of supposititious denudation of intermediate strata.

Any one or more of the geological formations may be entirely awanting in certain localities to a great extent, their places being supplied by, formations of a higher or lower level.

The whole series of geological formations could never be present in every portion of the earth's surface as long as there existed an ocean varying in depth.

Remarks on the Entomology of Angola with reference to the Geographical Distribution of Insects in Africa. By Professor ERICHSON of Berlin.

A CAREFUL and attentive examination of the manner in which the natural products of Africa are distributed, appears to us the only safe method by which we may establish our inferences re garding the condition of the unknown interior of this colossal Continent, on a broader and more sold basis than can be expected from comparisons with other parts of the world, similarly formed and situated. The comparatively small quantity, of water transmitted to the sea from such an extent of country, and which, contrasted with the numerous and gigantic streams of Asia and South America, seems very inconsiderable, has long been a matter of surprise. Nevertheless, some geographers imagine that the desert-girt interior of Africa is traversed by immense mountain chains. It becomes of course necessary to suppose, that the greater portion of the atmo-. spheric vapours, condensed by the action of these great moun-tains, is carried to inland-lakes, the size of which must be so considerable, that their surface of vaporization will correspond, with the quantity of water received, since they have no communication with the sea. We readily confess that this view presents many interesting points, but it is impossible to reconcile it with the manner in which the various species of animals are distributed over Africa. The circumstance, that several species, for instance the ostrich, have spread from the

deserts of Arabia, and from the foot of the Atlas Mountains, as far as the Cape of Good Hope, is strongly in favour of the hypothesis, that the whole of Central Africa, so far from being traversed by chains of lofty mountains, presents nothing but a series of sandy plains and deserts. The existence of the former would certainly prove an insurmountable barrier to the ostrich, though we are less positive with regard to the simi larly distributed lion and elephant.

Our argument derives, however, the most solid and the most substantial support from an examination of the manner in which the various Faunas are distributed over the Continent of Africa. Generally speaking, the want of variety amongst them is very striking. In Asia the towering mountains of the Himalayah distinctly separate the Indian Fauna from that of Central and Northern Asia; and their respective Faunas are so unlike each other, that they scarcely admit of comparison. In a similar manner, the Andes of South America divide the Faunas of the eastern districts from those of the western provinces; and it is in vain to look for points of resemblance between the two. This is certainly not the case in Africa. The Faunas of Nubia and of Senegambia are materially the same, even as regards the identity of a vast number of species. So close a relationship between the Faunas of opposite coasts. could hardly be accounted for, on the supposition that immense masses of mountain ranges, like those of the Himala yah, of the Andes, or even of our Alps, are interposed. Accordingly, if it can be proved that there exist similar relations between the various districts of Africa, which lie remote from each other; and that their Faunas are intimately connected with one another, not only in the directions of geographical longitude or latitude, but likewise in that of the diagonal; the well: known hypothesis of Lacepede, according to which the interior of Africa is said to consist of a vast collection of mountain. chains, is then completely refuted on the other hand, the opinion of Professor Ritter becomes more firmly established, according to whom the interior of Africa is a large table-land encompassed by ranges of hills, and no doubt interspersed with mountains, but which are so loosely united, and of such secondary importance, that the Faunas may easily traverse them in

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