[ 508 ] 

 LXXV. Proceedings of Learned Societies, 



GEOLOGICAL SOCIETY. 



Anniversary Address of the Rev. Prof. Buckland, President, 



Feb. 21, 1840. 

 [Continued from p. 396, and concluded.] 



POSITIVE GEOLOGY. DEVONIAN SYSTEM. 



IN the Home Department of Positive Geology, the most striking 

 circumstance has been an announcement by Professor Sedgwick 

 and Mr. Murchison of the conclusion to which they were led bv 

 Mr. Lonsdale's suggestion in December 1837, founded on the inter- 

 mediate character of the fossils in the Plymouth and Torbay lime- 

 stone that the greater part of the slate rocks of the south of Devon 

 and of Cornwall belong to the old red sandstone formation. 



The order of the observations which have led to this important 

 result, is nearly as follows : 



In a paper read at Cambridge, during the winter of 1836-37, 

 Professor Sedgwick considered the fossiliferous slates on both sides 

 of Cornwall to be of the same formation, and coeval, or nearly so, 

 with the calcareous rocks that lie between the slates of South 

 Devon. 



In 1836 and 1837 also*, Messrs. Sedgwick and Murchison pro- 

 posed to transfer the culmiferous or anthracitic shale and grits (Shil- 

 lot and Dunstone) of North Devon to the carboniferous system ; 

 withdrawing them from the grauwacke in which they had before 

 been included, and thus assigning a much more recent date than 

 heretofore to the strata which occupy nearly one third part of the 

 map of Devonshire. 



But the relations of the slates and limestones of South Devon still 

 remained to be determined ; the mineral characters of the former 

 being different from those of the old red sandstone beneath the car- 

 boniferous group, in many parts of South Wales and in Hereford- 

 shire, while the true position of the limestones (e. g. those of Ply- 

 mouth, Torbay, and Newton Bushell,) was doubtful. At this period 

 (1837), the fossils of this district were examined by Mr. Lonsdale 

 and Mr. Sowerby, to whom the organic remains, both of the car- 

 boniferous and Silurian systems, were familiar. It was soon per- 

 ceived, that while some of the South Devonshire fossils approached 

 to those of the carboniferous strata, and others to those of Siluria, 

 there were still many species which could not be assigned to either 

 system ; the whole, taken together, exhibiting a peculiar and inter- 

 mediate palaeontological character. Mr. Lonsdale therefore sug- 

 gested, that the difficulties which had perplexed this inquiry could 

 be removed by regarding the limestones of South Devon as subor- 

 dinate to slaty rocks, which represent the old red sandstones of Here- 



* In August 1836, at the Meeting of the British Association at Bristol; 

 and in a paper read before the Geological Society, May and June, 1837. 

 now published in the Geological Transactions, Second Series, vol. v., Part 3, 



