1870.] -VYOOD — WEALD -VALLEY DENUDATION. 3 



Irish floras. Prof. Heer had been led, chiefly by the erroneous de- 

 termination of the Kiltorkan Lepidodendron by the Irish palseonto- 

 logists, 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 classi- 

 ficatory purposes. He mentioned forms of vegetable life assigned 

 by Dr. Heer to the miocene which had reaUy 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 ques- 

 tion arose whether there had been any change in the position of the 

 Pole or whether the heat radiated by the earth was sufS.cient to 

 render an Arctic climate equable in Palaeozoic times. 



2. On the Evidence afforded by the Detrital Beds without and 

 within the North-easteen part of the Yalley 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 off'throw 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 pro- 

 minently into notice the fact that a large part of the debris con- 

 tained 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 denu- 

 dation 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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