510 Geological Society : Anniversary Address. 



Mr. Austen, in a communication relating to the structure of the 

 south of Devon, has identified the calcareous slate and limestone 

 of the south of Cornwall with the limestones of this district, and con- 

 siders that of Torbay among the newest deposits in the latter series. 



The Rev. D. Williams also has communicated two papers re- 

 specting these disputed rocks, which he refers to the transition 

 or grauwacke system, and endeavours to show that the strata of De- 

 vonshire can be distinguished into certain groups by their litholo- 

 gical characters. 



Mr. De la Beche in his map of Devon and Cornwall, published 

 in 1839, has adopted divisions of the strata, similar to those of Pro- 

 fessor Sedgwick and Mr. Murchison, as to their order of sequence ; 

 applying, provisionally, to the culmiferous rocks the name of Car- 

 bonaceous series, and to the Devonian and Cornish slates the appel- 

 lation of Greywacke. 



We know also on the authority of Mr. De la Beche that tin mines 

 are worked in carbonaceous rocks at Owlescomb near Ashburton, 

 on the east side of the Dartmoor granite, and on its west side at 

 Wheal Jewel near Tavistock. He further informs us that one of 

 the richest tin mines now worked in Cornwall, namely the Charles- 

 town mine, east of St. Austle, is in a fossiliferous rock containing 

 Encrinites and corals, and that the same corals occur also near tin 

 mines at St. Just ; and in the neighbourhood of Liskeard the Rev. 

 D. Williams has found slates which contain vegetable impressions, 

 dipping under other slates which are intersected by lodes of tin and 

 copper. 



From these new facts, we learn that the killas and other slate 

 rocks of Cornwall and the south of Devon do not possess the high 

 antiquity which has till lately been imputed to them ; and that tin 

 occurs, as copper, lead and silver have long been known to do, not 

 only in slate rocks that contain organic remains, but even in the 

 coal formation. 



Soon after the publication of the views of Messrs. Sedgwick and 

 Murchison, a similar change was applied by Mr. Griffith to the 

 south-west portion of his geological map of Ireland. In a paper 

 that accompanied the presentation of this map to us on 22nd of 

 May last, he states that he has now coloured, as old red sandstone 

 and carboniferous limestone, extensive districts of the counties of 

 Kerry, Cork, and Waterford, previously considered of higher anti- 

 quity ; imputing his former erroneous opinion to the identity in 

 lithological character of the shales aad grits of the old red sand- 

 stone and carboniferous systems, with the older rocks in the transi- 

 tion series. 



Mr. Griffith has also demonstrated by sections the unconform- 

 able position of the carboniferous and old red sandstone formations, 

 which overlie older and more highly inclined slates in the counties 

 of Kerry, Cork, Waterford, and Wexford. 



Mr. Charles William Hamilton has likewise adopted similar 

 changes ; and believes that the slates which occupy a large space 

 between the Mourne Mountains and Dublin are equivalent to those 

 near Cork, which he now transfers to the old red sandstone. 



