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Show 302 EOCENE PERIOD. [Ch, XXI. and west and of which there are many in the Weald district, parallel t'o the central axis of the Forest r1'd ge. In whatever manner the transverse gorges originated, they must evidently have formed ready channels of communication between the submarine longitudinal valleys and those deep parts of the sea wherein we imagine the tertiary strata to have been accumulated. If the strips of land which fit·st rose had been unbroken, and there had been no free passage through the cross fractures, the currents would not so easily have drifted away the materials detached from the wasting cliffs, and it wou.ld have been more difficult to understand how the wreck of the denuded strata could have been so entirely 8\Vept away from the base of the escarpments. In the next chapter we shall resume the consideration of these subjects, especially the proofs of the former continuity bC the chalk of the North and South Downs, and the probable connexion of the denudation of the W cald valley with the origin of the Eocene strata. CIIAPTER XXII. Denudation of the Valley of the Weald, continued-The alternative of the proposition that the chalk of the North and South Downs \Vere once continuous, considered-Dr. Buckland on the Valley of Kingsclere-Rise and denudation of ~econdary rocks grauual-Concomitant depoRition of tertiary strata gradual -Composition of the latter such as WOllld re~ult from the wreck of the secon· dary rocks-Valleys and furrows on the chalk how causcd-Auvl'rgne, tho Paris basin, and south-east of England one region of earthquakes rlming the :Eocene period-Why the central parts of the London and Hampshire basi us rise nearly as high as the denudation of the V\'ea.ld-Effects of protruding fo1·ce counteracted by the levelling operations of water-Thickness of ma~ses removed from the Cl!ntral ridge of the 'Weald-Great escarpment of the chalk having a direction north-east and south-west-Curved and vertical struta in the Isle of Wight-These were convulsed after the deposition of the fresh-water bells of lleaden Hill-Elevations of land posterior to the cmg-·why no Eocene alluviums recognizable- Concluding remarks on the intermittent operations of earthquakes in the south-cast of England, and the gradual formation of valleys -Recapitulation. Extent of denttdalion in the Palley of the Weald.-' I-r would be highly rash,' observes Mt·. Conybeare, speaking of the denu~ dation of the Weald, 'to assume that the chalk at any period actually covered the whole space in which the inferior strata are now exposed, although the truncated form of its escarpment evidently shows it to have once extended much farther than at present*.' We believe that few geologists who have considered the extent of country supposed to have been denuded, and who have explored the hills and valleys of the central, or Forest l'idge, without being able to discover the slightest vestige of chalk in the alluvium t, will fail to participate, at first, in the doubts here expressed as to the original continuity of the upper secondary formations over the anticlinal axis of the Weald. For our own part, we never traversed the wide space which separates the Nol'th and South Downs, without desiring to escape from the conclusions advocated in the last chapter; and yet we have * Outlines1 p. 144. t See above1 p. 295. |