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Show 298 EOCENE PERIOD. [Ch. XXI. Eocene period. Hence these flints might naturally occur on the downs, and be wanting in the valleys below· If the reader will refer to the preceding diagrams (Nos. 69 and 70), and reflect not only on the successive states of the country there delineated, but on all the intermediate conditions which the district must have passed through during the process of elevation and denudation before supposed, he will understand why no wreck of the chalk (No. 1) should occur at great distances from the chalk escarpments. For it is evident that when the ruins of the uppermost bed (No. 1, diagram 69) had been thrown down upon the surface of the bed immediately below, those ruins would subsequently be carried away when this inferior stratum itself was destroyed, And in proportion to the number and thickness of the groups, thus removed in succession, is the probability lessened of our finding any remnants of the highest group strewed over the bared surface of the lowest. Transverse valleys.-There is another peculiarity in the geographical features of the south-east of England which must not be overlooked when we are considering the action of the denuding causes. By reference to the map (Plate 5), the reader will perceive that the drainage of the country is not effected by water-courses following the great valleys excavated out of the argillaceous strata (Nos. 2 and 4), but by valleys which run in a transverse direction, passing through the· chalk to the basin of the Thames on the one side, and to the English channel on the other. In this manner the chain of the North Downs is broken by the rivers Wey, Mole, Darent, Medway, and Stour; the South Downs by the Arun, Adur, Ouse, and Cuckmere*. If these transverse hollows could be filled up, all the rivers, observes Mr. Conybeare, would be forced to take an easterly course, and to empty themselves into the sea by Romney Marsh and Pevensey levels t. "' Conybeate1 Outlinea o£ Geol., p. 81. t Ibid., p. 145. Ch, XXI.] TRANSVER~E VALLEYS. 299 Mr. Martin has suggested that the great cross fractures of the ., t . 2 ~ ~·~ 2 .0..0. 0 chalk which have become river channels have a remarkable correspondence on each side of the valley of the Weald ; in several instances the gorges in the North and South Downs appearing to be directly opposed to each other. Thus, for example, the defiles of the Wey, in the North Downs, and of the Arun in the South, seem to coincide in direction; and, in like manner, the Ouse is opposed to the Darent, and the Cuckmet ·e to the Medway*. But we think it very possible that these coincidences may be accidental. It is, however, by no means improbable, as hinted by the author above mentioned, that the great amount of elevation towards the centre of the Weald dis-c: l ~ trict gave rise to transverse ~r fissures. And as the longitu-dinal valleys were connected with that linear movement which caused the anticlinal lines running east and west, so the cross nssures might have been occasioned by the intensity of the upheaving force towards the centre of * Geol. of Western Su11sex1 p. 61, |