and conglomerate or pebble beds formed of the detrital flints. The mass of igneous rocks poured out on the chalk of Ireland, is of too indefinite an age to be appealed to as proof of convulsions in that quarter. But on the continent of Europe, De Beaumont assigns to this period his Pyreneo-apennine system of convulsion,-the elevation of the Pyrenees, Carpathians, Northern Apennines, Dalmatia, and the Morea, in lines ranging parallel to a great circle on the sphere through Natchez and the Persian Gulf. It appears also that some disturbances which happened during the cretaceous era, are traceable in Mont Viso and the Western Alps. Supposing the Pyreneo-apennine system to be principally, if not wholly referrible to this period, we seem to behold a reason for the agitation of the shores of the English chalk basin; the distant convulsion might sufficiently explain this local and transient agitation, but, in fact, it is very probable that the English chalk underwent a gradual local elevation, which contracted the area of the bordering seas, and formed shores and dry land slopes of chalk, to be wasted by the waves, the rivers, and the rains. The pebble-beds of the tertiaries which rest on the chalk of England, do indeed more exactly correspond to such an origin than to the effect of sudden and violent disturbance.

AB

Base of the Strata.-We have seen that during the long and yet unmeasured period which elapsed during the accumulation of the secondary strata, elevation of the land continually happened by gradual forces, and sometimes by violent disturbance. The most striking case of the latter

is the general disruption of the coal system, at least before the completion of the red sandstone deposition. Of the gradual elevation of strata, almost the whole series furnishes continual proof. Hence it is, that the oolitic rocks follow one another so exactly in their geographical boundaries, retiring continually into smaller and narrower areas, as the elevation of the old land proceeded. In the continuation of the process, the greensand and chalk form, at least in England and France, a still interior band of deposits, which mark the gradual contraction of the seas, that is, the gradual uprising of the land.

The tertiary strata have, in general, to the chalk the same geographical relations as that to the oolites. Throughout England, the chalk is the base of all the tertiary strata. In France this is generally the case, and almost universally so for the marine tertiaries. In the north of Germany, along the north and south slopes of the Alps, and in the basin of the Danube, this is at least very extensively true. In North America, the general basis of the tertiaries is the cretaceous formation. On more close inquiry, it appears, however, that the tertiary strata are seldom exactly conformed to the stratification of the chalk; that any thing like a gradation or alternation of the cretaceous into tertiary deposits, is rarely known; that the organic remains of the one group differ almost wholly and absolutely, except in the south of France, at Maestricht, &c., and constitute two distinct groups of created life. Hence it has become a popular opinion, that with the secondary strata ended a certain general condition of the globe, and with the tertiaries commenced a totally new arrangement. Moreover, because we find the marine tertiary strata distinctly related, in geographical expansion, to the present basins and arms of the

ocean; as the organic remains which they contain are similar, and, in rocks of later date, identical to those of the existing races in the sea and on the land; and as the tertiary sediments are of a nature very analogous to the daily products of the sea, estuaries, tide-rivers, and lakes,—there is but a step farther to unite the tertiary era with the historical period of the globe, and to place the commencement of the actual creation or arrangement of organic nature at the epoch immediately following the chalk. For these and other reasons, the tertiary strata are of great interest. They admit of a clear comparison, in all respects, with the effects which daily occur before our eyes; and thus facilitate our inquiry into the conditions of nature in earlier periods. They furnish the principal arguments on which Mr Lyell rests his doctrines of the continual uniformity of the measure of terrestrial agencies, as the older strata have long done to those who maintain that, in the construction of the crust of the globe, periods of ordinary action have been broken by crises of unusual violence.

Nature of the Tertiary Strata.-In very few instances, during our survey of the products of earlier nature, have we found reason to admit the deposition of strata in any other waters than those of the sea, in its depths and along its shores. The coal deposits of the north of England generally belong to the class of estuary formations, in which the influence of the sea was often less and never more sensible than in the bed of a tide-river, where the water is only brackish. At intervals, indeed (Yorkshire coal-field), when. great distant disturbance or local change of the circumstan ces occurred, the influence of the sea has returned and produced its usual effects, leaving, as monuments of its short dominion, peculiar kinds of animal exuviæ.

The oolitic formation on the Yorkshire coast and in Sutherland proves plainly enough the local addition of fresh waters and spoils from the land; the Wealden formation indicates, in like manner, a wide estuary fed by some river, on whose banks gigantic reptiles or tropical plants abounded; but nothing has yet been shewn with respect to any carboniferous or oolitic deposit, which renders necessary the supposition of lacustrine or purely fresh-water deposits. Communication with the sea from the basins of the coal deposits, and from the Wealden beds, is apparently indis pensable in explaining the occurrence of particular sorts of fishes in these strata, and not in any respect inconsistent with the evidence of the molluscous exuviæ. The most plausible arguments for fresh-water deposits among the older strata, are advanced by Dr Hibbert in his description of the Burdiehouse fossils, and by Mr Murchison in his notices of Shropshire coal-fields. Without in the least wishing to intimate that the influence of fresh-water in accumulating the materials of the strata is most conspicuous in the newer strata,—an inference not justifiable by the facts, -it is to be remarked, that the deposition of stratified rocks in limited basins of fresh-water is a phenomenon almost characteristic of the tertiary period.

The same tracts of watery surface beneath which the coalfield of Yorkshire was formed suffered alternate influence of the sea and river water. The estuary of the Wealden, and the coal deposit of the oolitic hills, were alike formed upon the bed of formerly deep seas, and at a later period deep sea again covered the same area: in a certain sense, the deposits of fresh and salt water alternate in several secondary formations. But in the tertiary strata, this phenomenon of alternating marine and fresh-water products is more decided

and remarkable. In the basin of Paris, at least two freshwater and two marine deposits alternate in the tertiary series. Alternations of really fresh-water and really marine products happen in the south of France, the valley of the Rhine, in Hungary, and the Isle of Wight. In these cases the explanation is possible, without supposing repeated upliftings and submersions of the land—of which, from other phenomena, there is no evidence-by merely conceiving estuaries or expansions of water, such that the influence of rivers and the sea might alternately predominate, just as, in fact, we know to have happened, even in historical times, in the marshes of East Norfolk,-and as must have 'often occurred in similar tracts at the mouths of rivers where variable sand-banks abound, and alter the direction of littoral currents. At some later epoch, the whole bed of the estuary has been uplifted to its present elevation above the sea.

Nature of the Marine and Fresh-water Deposits.—It is a remarkable confirmation of the views of modern geologists, that a great portion of the substance of sedimentary strata was swept down to the sea by inundations and other watery forces operating on the surface of the dry land,-that the marine and fresh-water sediments of the tertiary era have so much general analogy. In each we have calcareous, argillaceous, and arenaceous deposits, alternating,—stratified, laminated, in a similar manner; the organic exuviæ are similarly disposed in the beds, and, but from the character of these, we could not in general venture to pronounce upon the nature of the water in which the beds were deposited. Some distinction is, however, to be traced; the marine arenaceous sediments are thicker and more confused than those of fresh-water; the marine clays are less minutely laminated. It may be remarked, in general, that