516 I\lli. W. A. E. rSSHER ON THE DEVONIAN 



From what Professor Gosselet has shown me in the Ardennes, 

 and on a brief visit to the Eifel, I was greatly struck with the 

 comparatively recent appearance of the Upper-Devonian shales, 

 which reminded me more of weathered Lias- and Oolite-shale, and 

 of llha^tic shales, in places, than of any Upper-Devonian slates in 

 Devonshire, where the rocks are much more indurated, compressed, 

 and cleaved. The same phenomenon is exhibited by the Eifelian 

 slates of Couvin and of Gerolstein on comparison with the slates of 

 Berry Park and Mudstone Bay. 



In the Lower-Devonian of the Gerolsteiner-AVald, I recognized 

 similarities to Lower-Devonian rocks in N'orth and South Devon : 

 and in the Lower-Devonian slate types of St. -Hubert, Oignies, and 

 Mondrepuits, in the Ardennes, near Pumai, I detected a great 

 resemblance to the Dartmouth slates. In fact, in the districts where 

 the rocks had undergone the greatest disturbance the similarity to 

 those of Devon seemed to be the most pronounced. 



As regards South Devon, the facts established in this paper have 

 a much wider application than to the district described ; for De la 

 Beche's Map and the E-eport (pp. 76-79), referring to the geology 

 of the district from the Dart southward to Plymouth, will show the 

 existence of extensive areas of Lower Devonian (Cockington beds) 

 from Morleigh Down and Black Down to the coast at Erme Mouth, 

 and at Staddon heights and Modbury. 



I conclude with the following quotations from Mr. Champer- 

 nowne's iSTotes on the Ashprington series, when referring to the 

 relations of the volcanic materials to the limestones : — " all these 

 anomalous appearances are at the same time quite capable of being 

 accounted for, if we consider what might take place in a reef 

 district which was at the same time the arena of volcanic dis- 

 turbance." 



Referring to the difficulty in distinguishing the slates below from 

 those above the limestone, he says: — "But why should there not 

 also be slates neither exactly above nor below the limestone, but 

 replacing it ? So that De la Beche's words would also be true, viz. 

 that ' the geological continuation of certain limestones appears to 

 consist of slate '" *. 



Discussion. 



The Pkesident referred to the late Mr. Champernowne's paper on 

 the Ashprington Series, and to the maps presented by that geologist 

 to the Geological Survey. The task of dovetailing the Survey-maps 

 with those of Mr. Champernowne was entrusted to Mr. Ussher, 

 who had now for the first time made a careful comparison between 

 the rocks of South Devon and those of the Continent. Dip and 

 strike went for little in such plicated and dislocated countries as 

 that which the Author had surveyed, but he had with great patience 

 and success pieced together the fossil evidence, and had thus brought 



* Quart. Journ. Geol. Soc. vol. xlv. p. 377. 



