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Show EOCENE PERIOD. [Oh.XX. These newer strata of the Isle of 'Vight bear a certain de .. gree of resemblance to some of the green marls and limestones in the Paris basin, yet, as a whole, no formations can be more dissimilar in mineral character than the Eocene deposits of EnO'land and Paris. In our own island the tertiary strata are mo;e exclusively marine, and it might be said that the Parisian series differs chiefly from that of London in the very points in which it aO'rees with the formations of Auvergne, Cantal, and y ela y. ;he tertiary formations of England are, in factJ almost exclusively of mechanical originJ and their composition be. s eaks the absence of those mineral and thermal waters to ~1ich we have attributed the origin of the compact and siliceous limestones, the gypsum, and beds of pure flint, common to the Paris basin and Central France. English tertiary sb·ata conformable to thechallc.-TheBritish Eocene strata are nearly conformable to the chalk on which they rest, being horizontal where the stra:a of the chalk are horizontal, and vertical where they are vertical. On the other hand, there are evident signs that the surface of the chalk had, in many places, been furrowed by the action of the waves and currents, before the Plastic clay and its sands were superimposed. In the quarries near Rochester and Gravesend, for instance, fine examples are seen of deep indentations on the surface of the chalk, into which sandJ together with rolled and anO'ular pieces of chalk-flint, have been swept *. But these ap;earances may be referred to the action of water when the chalk began to emerge during the Eocene period, and they by 110 means warrant the conclusion, that the chalk had undergone any considerable change of position before the tertiary strata were superimposed. In this respect there IS a marked difference between the reciprocal relations of our secondary and tertiary rocks and those which exist between the same groups throughout the greater part of the continent, especially in the neighbourhood of mountain-chains. Near the base, for example, of the Alps, * Con. and Phil.1 Outlines of Geol., p. 62, Ch. XX.] TERTIARY OUTLIERS ON CIIALI{, 283 Apennines, and Pyrenees, we find the newer formations reposing unconformably upon the truncated edges of the older beds, and it is clear that, in many cases, the latter had been subjected to a complicated series of movements before the more modern strata were formed. The latter rise only to a certain height on the flanks of the mountains which usua11y tower above them, and are recognized at once by the geologist as having been upraised into land when the tertiary formations were still forming in the sea. The ancient borders also of that sea can often be defined with certainty, and the outline of some of its bays and sea-cliffs traced. In England, although undoubtedly the greater portion of the tertiary strata is confined to certain spaces, we find outlying patches here and there at great distances beyond the general limits, and at great heights upon the chalk which separates the basins of London and Hampshire*. I have seen masses of clay extending in this manner to near the edge of the western escarpment of the chalk in Wiltshire, and Mr. Mantell has pointed out the same to me in the South Downs. Near the escarpment at Lewes, for example, there is a fissure in the chalk filled with sand, and with a ferruginous breccia, such as usually marks the lower members of the Plastic clay for .. mation. From the fact of these tertiary outliers Dr. Buckland inferredJ 'that the basins of London and Rants were originally united together in one continuous deposit across the now intervening chalk of Salisbury Plain in Wilts, and the plains of Andover and Basingstoke in Rants, and that the greater integrity in which the tertiary strata are preserved within the basins has resulted from the protection which their compara~ tively low position has afforded them from the ravao-es of dilu-vial denudation t.' 0 We agree so far with this conclusion as to believe that the basins of L.ondon and Hampshire were not separated until part of the tertiary strata were deposited, but we do not think it probable that the tertiary beds ever extended continuously over * Dr, Buckland, Geol. Trans., Second Series, vol. ii.p. 125. Ib'd t 1 .,p. 126. |