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Show 342 RELATIVE ANTIQUITY [Ch. XXIV, elevation at a certain epoch in the earth's history, namely, between the deposition of the chalk and that of the tertiary formations ; for the former are seen in vertical, curved, and distorted beds on the flanks of the chain, while the latter rest upon them in horizontal strata at its base. The only proof offered of the extreme suddenness of the convulsion is the shortness of the time which intervened between the formation of the chalk and that of the tertiary strata. 'For it 'follows,' we are told,' from the unconformable position of two systems of beds, the inclined and the horizontal, that the elevation of the former has not been effected in a continuous and progressive manner, but that it has been produced in a space of time comprised between the periods of deposition of the two consecutive rocks, and during which no 1·eO'ular series of beds was formed; in a word, that it was sudden b and of short duration *.' We are prepared to show that the Pyrenees cannot be assumed to have risen, as M. de Beaumont imagines, in the interval between the period of the chalk and that of the tertiary strata; for we can only say that the movement took place after the commencement of the chalk epoch, and before the close of the Miocene tertiary period. But, first, let us suppose the premises of our author to be correct, and let us permit him to exclude the whole period of the chalk, on one hand, and of the tertiary formations in contact with it on the other; what will then be the duration .of the interval? We can only estimate its importance by ascertaining what description of chalk is found on the flanks of the Pyrenees, and what horizontal tertiary formations at their base. Now the beds called chalk, although they differ widely in mineral composition from the white chalk with flints of England and France, contain the same species of fossil shells, and may, therefore, on that evidence, be referred to the same age t. On the other hand, the horizontal tertiary strata at the * Phil. Mag. and Annals, No. 58, new series, p. 243. t The fossils which I collected in company with Captaiu S, E. Cook, R. N.t Ch.XXIV.] OF MOUNTAIN-CHAINS, 343 wester~ end of the Pyrenees, near Bayonne, are certainly of the Mwcene period. Such, then, being the age of the strata, and granting even that the movement occurred after the period of the white chalk, and before the beginning of the Miocene era, there still remains ample scope for conjecture as to the date of the event. For the up~eaving of the Pyrenees may have been going on when the ammals of the Maestricht beds flourished, or during the indefinite ages which may have elapsed between their extinction and the introduction of the Eocene tribes, or during the Eocene epoch, or between that and the Miocene. Or the rise may have been going on continuously throughout several or all of these periods. ~ut this is ~ot all; we m~st include within the possible space of time wherein the convulsiOns may have happened, part of the epochs both of the chalk and of the Miocene species. We have stated, that the newer Pliocene beds in Sicily have been raised during the newer Pliocene epoch, partly, perhaps, in the Recent, but this latter supposition will lend equal support to our present argument. Now, it is evident that the greater part of the species of testacea which pre-existed in the Mediterranean have survived the elevation of the newer Pliocene beds in Sicily, and in the same manner there is no reason to conclude that the rise of the chalk in the Pyrenees exterminated the animals which lived in the sea wherein the chalk was formed. In that case, a series of con.vulsions may not only have begun, but may even have been completed before the era when the Maestricht beds originated. In like manner the sea may have been inhabited by Miocene testacea for ages before the deposition of those particular Miocene strata which occur at the foot of the Pyrenees and the disturbing forces may have operated in the Miocene p:riod, from ~he newest secondary beds on the flanks of the Pyrenees, near Bayonne, were exa~med by M. Deshayes, and found identical with sllecies of the chalk near Pans. . |