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by the production of the central mountain districts of Europe and Asia. In this way was given the first decided tendency to the great east and west line of direction which was afterwards retained during the elevation of the eastern part of the northern hemisphere.
How long it was after the deposit of the chalk that these movements commenced, and how long they lasted,-whether, as is probable, they began early, and lasted for a very long time, or whether they commenced only when the chalk had become hard and attained its present condition,—we are not able yet to assert; but there is little doubt that the great secondary period was locally terminated by disturbances connected with the elevation of Europe and Asia, while possibly at this very time deposits were going on in the seas immediately adjacent, and over a great part of the valleys in those two continents.
These, we believe, are conclusions which Geologists will hardly be inclined to dispute, and they form the outline of a connected history of the revolutions of the globe during the secondary epoch. But, besides that part of the history which has immediate reference to British Geology, there are other important facts already known with reference to other districts. The successive elevation of the Alps, the Pyrenees, the Carpathians, the Caucasus, and the Himalayan chain, and even of the Andes, will also be found to bear importantly on the general physical Geology of the epoch, and will tend to clear up many doubts and difficulties that arise in the contemplation of the phenomena as they are presented in our own country and in western Europe.
THE THIRD, OR MODERN EPOCH.
THE INTRODUCTION OF LAND ANIMALS AND THE COMMENCEMENT OF THE TERTIARY PERIOD IN WESTERN EUROPE.
THE close of the secondary period was succeeded by a general disruption of the various beds that had been deposited in those parts of the earth to which we now have access, and by changes and modifications so considerable as to alter the whole face of nature. It would appear, also, that a long period of time elapsed before newer beds were thrown down, since the chalky mud not only had time to harden into chalk, but the surface of the chalk itself was much rubbed and worn.
So completely and absolutely is the line of demarcation drawn between the secondary and newer deposits in parts of the world where these beds have been recognised in actual contact, that it had become a common notion among Geologists, to assume the destruction of all natural relations between them, concluding that not one single species of animal or vegetable connected the two periods, and lived through the intervening disturbances. Although this view certainly requires modification in points of detail, it
is still correct in a general sense, and expresses, without much exaggeration, the real extent of difference in condition, the result, perhaps, a lapse of time greater than is elsewhere indicated. In this way the secondary period is distinctly cut off from the tertiary. It is scarcely less separated by the fact that in the former we every where find marks of the presence or near vicinity of the sea in all the deposits, even those from fresh water, while, in the newer beds, land animals at once assume the importance which they have ever since retained, having been evidently present in great numbers and variety.
Confining ourselves, at present, to the principal localities of older tertiary deposits in Europe, we find distinct indications, from the nature of the beds themselves, that they were deposited with a considerable degree of regularity, and even uniformity, and not in a very short time. The beds are extensive, and consisted at first of such rolled pebbles as might have been produced by the rubbing and wearing of the chalk flints on a shingle beach. The rocks were broken into small and similar fragments, rolled until they were perfectly smooth and either round or oval, and thus appear of nearly uniform character throughout widely distant tracts. Whatever, therefore, was the condition of the district now covered by the older tertiary beds of England, France, and Belgium, during those ages that elapsed between the final deposition of the chalk as we now see it, and the deposit of pebble-beds upon its worn surface, the cause that brought into existence these beds seems to have been connected with the re-introduction of a coast-line, and a shallow adjacent sea-bottom. Whether, as is
highly probable, a deep sea at first covered all these districts, and, owing to comparatively rapid and repeated elevation after the deposit of the chalk, the change of depth destroyed, without allowing to emigrate, the species of animals of whatever kind that inhabited the ancient sea, or whether a considerable tract of land was formed in an east and west line, cutting off communication between districts not far removed in latitude, and extending, perhaps, from Asia Minor far out into the Atlantic: these are points which Geology does not, at present, enable us to solve. All we know is the great fact of the absence of the chalk species in the tertiary beds, their place being supplied by new species, for the most part of very different organization. We thus have to enter upon a new series of phenomena, when we turn from the contemplation of the secondary to that of the tertiary period.
When, however, the time had elapsed, and the change had taken place, and it must be repeated that the interval, whether long or comparatively short, was marked by the destruction of nearly the whole marine creation, —when, after this, the seabottom in these parts of the world again received accumulations of mud and shingle, it is not unlikely that a great elevatory movement had already commenced. From the general direction of the subsequent disturbances which brought to light the Wealden district in England, and elevated the Alps and the Caucasus, it is almost certain that the line of that movement was, on the whole, east and west.*
* The later, or tertiary movement, seems to have had a north-west and south-east direction, as the former one, effecting the elevation of the oolites
From the careful examination of Europe, as it now exists, we also learn that the elevation was most considerable in the middle of Europe, extending thence to the western part of England along what is now its southern coast; marked by a parallel movement in the line of the Pyrenees, the corresponding range on the east coast of the Adriatic, and the Caucasus, and producing land inclosing lakes of fresh water in what is now the Grecian Archipelago.
It appears, also, that these disturbances were continued until the close of the middle tertiary period in central Europe, and probably much later in the Caucasus, while they have, perhaps, scarcely yet ceased in the central parts of Asia. They were, however, much earlier concluded in England, and were there succeeded by a long period of tranquillity, our own island being elevated above the sea, and receiving very slow additions, chiefly on its eastern coast.
In examining the Geology of the tertiary period we are fortunate enough to find a chain of evidence informing us not only of the existence of land, but of the nature of the vegetation that clothed it, and the animals that inhabited it. This evidence commences even before the beginning of the great disruption which brought up the Weald, and it lasts not only through the period of that disturbance, but afterwards to much later times. Owing, however, to the prevalence of causes which did not permit the preservation of organic remains, we have less evidence with regard to some of the later periods than to those of earlier date. There seems no doubt that the marine
of England, was north-east and south-west. The Alps form the central or culminating point, and are transverse to the main direction of the period.