Devonian System. 59 



1839 ; the authors then also proposing for the whole series (including both 

 the old red sandstones of Herefordshire, and the fossiliferous slates and 

 limestones of South Devon and Cornwall) the new name of " the Devo- 

 nian system," and expressing their belief that many of the groups hitherto 

 called greywacke, in other parts of the British Islands and on the Conti- 

 nent, would ere long be referred to the same geological epoch. 



The proposed alteration, therefore, will terminate the perplexity hitherto 

 arising from the circumstance that the old red sandstone of Werner has 

 been frequently confounded with the new red sandstone formation of Eng- 

 lish geologists. It also explains the cause of the English old red sand- 

 stone having been rarely recognised on the Continent : — for if the Devo- 

 nian slates afford the normal type of this formation, whilst the marly sand- 

 stones and conglomerates of Herefordshire are abnormal exceptions in it, 

 we see the reason why their slaty Continental equivalents, like the greater 

 part of the South Devon slates, have been referred to the undivided Wer- 

 ncrian formation of greywacke. 



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 considers that of Tor- 

 bay among the newest deposits in the latter series. 



The Rev. D. Williams also has communicated two papers respecting 

 these disputed rocks, which he refers to the transition or greywacke sys- 

 tem, and endeavours to shew that the strata of Devonshire can be dis- 

 tinguished into certain groups by their lithological 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 Professor Sedgwick 

 and Mr Murchison as to their order of sequence ; applying, provisionally, 

 to the culmiferous rocks the name of Carbonaceous series, and to the De- 

 vonian and Cornish slates the appellation of Greywacl:e. 



We know also, on the authority of Mr De la Beche, that tin-mines are 

 worked in carbonaceous rocks at Owlcscomb, 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 Charlestown 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 arc 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 con- 

 tain organic remains, but even in the coal-formation. 



Soon after the publication of the views of Messrs Sedgwick and Mur- 

 chison, a similar change was applied by Mr Griffith to the south-west 



