[ 396 ] 

 LX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xiv. p. 520.] 



April 10. — A PAPER was read, " On as much of the Transition 

 -t^- or Grauwacke system as is exposed in the counties 

 of Somerset, Devon, and Cornwall," by the Rev. David Williams, 

 F.G.S. 



The author commences by stating, that his views of the general 

 structure and arrangement of the country are original and independ- 

 ent, but that he does not in the least impugn the originality of the 

 observations and inferences of other geologists. He mentions, that 

 in a communication read before the British Association at Dublin 

 (1835), he used the following expression in remarking on the 

 broad outline of the structure of Devonshire with respect to the 

 relative position of the strata containing plants and culm : " the 

 clay slate (without the intervention of gneiss or mica- slate) dips 

 away from the granite of Lundy on the one hand, and from the 

 granite of Dartmoor towards it on the other ; " and that in a paper 

 sent to the Meeting of the British Association at Bristol (1836), but 

 received too late to be read, was inserted this passage : " the same 

 beds being brought up to the surface at either extremity " (Exmoor 

 and the north of Cornwall) " contain in their great intermediate 

 trough all the strangely contorted rocks and carbonaceous shales 

 we there witness." 



Mr. Williams then alludes to an error which he made in the paper 

 read at Dublin, by considering the mineral axis of Dartmoor to be 

 composed of the strata he calls the " Morte Slates," but which 

 he corrected in a paper read at Liverpool (1837) ; he notices also 

 another error which he had made in supposing that the same beds 

 (the Morte slates) were brought up among the granite of Dartmoor, 

 and which he did not discover till the spring and summer of 1838, 

 when he perceived that " the two superior members of the North 

 Devon group, Nos. 7. and 8. are brought up in the south in pre- 

 cisely the same order and relation in which they descend on the 

 north," having previously overlooked this natural simplicity of 

 arrangement. 



The chief objects of the paper are to show, that the strata can be 

 divided into certain groups, distinguished by weU-marked lithologi- 

 cal characters ; and that there is a gradual passage from the lowest 

 part of the uppermost or culm deposit into the series next below it, 

 and that similar passages are presented in each of the other underly-- 

 ing groups. To the intermediate strata the term neutral is applied. 



The whole of the beds are assigned to the transition or gray- 

 wacke class, and are arranged in descending order under the fol- 

 lowing nine heads, the topographical names being derived from the 

 localities where the strata are best exposed: — 9. Floriferous slates; 

 8. Coddon Hill grits; 7. Trilobite slates; 6. WoUacomb sand- 

 stones ; 5. Morte slates ; 4. Trentishoe slates ; 3. Calcareous slates 



