244 Prof. Sedgwick and Mr. Murchison on the Classification 



plants of the carboniferous system. On the same line are fer- 

 ruginous bands, with casts of shells, communicated by Major 

 Harding, which strongly reminded us of forms in the old Y*it\ 

 sandstone; one indeed being, as Mr. Sowerby thinks, identical 

 with the Bellcrophon globulus of that system *. 



In the next underlying groups of Morte Bay and llfra- 

 combe, we have few well-preserved mollusca, but among them 

 is a very wide Spirifer and a spined Productus, approaching to 

 the carboniferous type, but unlike anything we know in the 

 Silurian or Cambrian rocks. Corals occur in parts of these 

 Ilfracombe groups, and among them is the Favosiies poly- 

 viotpha, a species most abundant in the upper Silurian rocks, 

 but not found in the lower. 



Lastly, in the lowest group we perceived certain large heart- 

 shaped forms, quite unlike anything we had ever seen until we 

 afterwards detected the same in the collection of Mr. Hennah, 

 from the Plymouth limestone: and in the very lowest fossil 

 beds near Linton, we still perceived some of the same speci- 

 fic forms that occur near Barnstaple; which, though un- 

 described, may be pointed out as of characters intermediate 

 between those of the Silurian and carboniferous fossils, the 

 balance of evidence inclining rather to the younger of the two 

 types ; there being few if any traces of the genus Oi-this so emi- 

 nently characteristic of the Silurian system. These evidences 

 all tend one way, and (confirmed as they are by the passage 

 of the bottom culm-measures) force us to believe that the old- 

 est rocks of North Devon are much younger than we at first 

 supposed : and coupling these with other proofs still more co- 

 gent from South Devon, we arrived at the conclusion which 

 we shall presently explain. 



South Devon. — In the communication of 1837 to the Geo- 

 logical Society, we described several sections from the granite 

 of Dartmoor to the south coast of Devon, and (omitting the 

 altered slates) we divided the older stratified rocks into three 

 groups; the lowest, composed of slates, containing subordi- 

 nate bands of the A&hburton limestone, and ending in ascend- 

 ing order with the Plymouth and Torbay limestones, which 

 we considered to be identical ; the second, composed of red 

 sandstone, with occasional subordinate beds of shale, &c. ; 

 the third of soft non-fossiliferous schists, extending almost 

 to Start Point. These we considered (and we believe cor- 

 rectly) of the same age with the groups of North Devon ; 

 and we attempted (without the aid of fossils) to bring them 

 into close comparison, by identifying the great deposits o^ red 

 ■sandstone of the two districts. This identification of the sepa- 

 rate groups we cojisidered as merely provisional, " to be con- 

 * Murthisoii's Silurian System, PI. '6, 15. 



