Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/97

 Irish floras. Prof. Heer had been led, chiefly by the erroneous determination of the Kiltorkan Lepidodendron by the Irish palaeontologists, to refer these beds to the Carboniferous rather than to the Devonian formation, the Kiltorkan fossil having been established as a very distinct species by Brongniart and Schimper. Mr. Carruthers considered that both the Irish and Bear-Island deposits belonged to the Devonian.

Mr. Boyd Dawkins pointed out that the proximity of land was exhibited by the presence of terrestrial plants in the deposits, and prevented the correlation of the inshore deposits with those which were being formed in deep water. As the marine fauna changed more rapidly than the terrestrial flora, it was preferable for classificatory purposes. He mentioned forms of vegetable life assigned by Dr. Heer to the miocene which had really been discovered in America in beds of Cretaceous age. He did not believe that corals could have existed in those high latitudes under any thing approaching to the present conditions. Prof. Nordenskjold had failed to discover any traces of glacial action in these beds ; and the question arose whether there had been any change in the position of the Pole or whether the heat radiated by the earth was sufficient to render an Arctic climate equable in Palaeozoic times.

2. On the Evidence afforded by the Detrital Beds without and within the North-eastern part of the Valley of the Weald as to the Mode and Date of the Denudation of that Valley. By S. V. Wood, Jun., F.G.S.

[Plate I.]

The denudation of the Weald valley has long been a subject of interest and of contention among geologists. The theory of a rise of a dome of strata from beneath the sea and the offthrow of the waters on all sides from that dome, their escape through lateral fractures in the upheaved chalk, together with a slow wearing back of the fractured and denuded edges of the chalk in the form of cliffs, long held its ground in our text-books, and it is only of late years that this theory has met with partial dissent.

Sir Roderick Murchison was the first*, I believe, to bring prominently into notice the fact that a large part of the debris contained within the denuded area consisted of angular chalk flints brought from the exterior into the inner part of this area, and so far therefore was at variance with the received hypothesis of a flow of the denuding waters outwards from the exposed subcretaceous strata, over the surface of which these flints were scattered. His view, after an elaborate description of the detrital beds of, more especially, the western part of the great valley, was that the denudation had been accomplished by a powerful aqueous agent directed eastwards from the apex or western extremity of the Weald valley, by which these flints have been thus scattered over the Neocomian strata of that part of the valley.


 * Quart. Journ. Geol. Soc. vol. vii. p. 349.

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