and shape of the hind-Jin of the Ichthyosaurus. 71 



impressions. The structure of the integument of the fin agrees, 

 therefore, with the known reptilian characters of the skeleton of the 

 Ichthyosaurus ; and, as the skin with its appendages gives a charac- 

 ter to the great primary groups of vertebrata, it might be expected 

 that the skin of the Ichthyosaurus would exhibit some of the cha- 

 racters of the integument of existing reptiles. 



In conclusion, Mr. Owen remarks, that the other new facts pre- 

 sented by the specimen, accord with the indications of the natural 

 affinities of the Ichthyosauri afforded by their less perishable re- 

 mains ; and that all the deviations from the reptilian structure of 

 the skeleton tend to the type of fishes and not to that of cetaceous 

 remains. 



A paper was afterwards read on as much of the great graywacke 

 system as is comprised in the group of West Somerset, Devon, and 

 Cornwall, by the Rev. D. Williams, F.G.S. 



This communication is supplementary to one read in April 1839*, 

 and contains the results of the author's last investigation into the 

 structure of the country. Before he details his present views, he cor- 

 rects what he conceives was an error in his former paper, and states, 

 he is now convinced that the slates and limestones of South Devon 

 and Cornwall are not a prolongation of the trilobite slates (No. 7)f 

 of Exmoor, but a distinct formation superior to the floriferous grits 

 or culm measures (No. 9,) of central Devonshire, and consequently 

 the newest deposits of the country. For this formation he proposes 

 the name of Killas or Cornish, and he considers it as No. 10 in the 

 ascending series. According to the new arrangement therefore, in 

 proceeding from those parts of West Somerset bordering the Bristol 

 Channel to the south of Devon and Cornwall, he conceives a regular 

 ascending series is passed over, the central portion of which he is of 

 opinion, consists of the floriferous grit or culm measures (9). He 

 places the whole series also in the graywacke system. 



Mr. Williams's reasons for this arrangement are drawn from ob- 

 servations made at several localities in South Devon. 



At Doddiscombe Leigh, about four miles to the north of Chud- 

 leigh, the Posidonia limestone, a member of No. 8, the Coddon Hill 

 grit, underlies, Mr. Williams says, a long series of alternations, 

 exposed on the turnpike road towards Chudleigh, and consisting of 

 high hills of Coddon and floriferous grits with intercalated killas, 

 the whole dipping beneath the coral limestones of Chudleigh, which 

 pass under the ridge of Ugbrook considered by Mr, Williams to be 

 composed of floriferous grits. On closely examining the limestones 

 about Chudleigh, the author discovered minor alternations, which 



* See Proceedings, vol. iii., p. 115, [or L. & E. Phil. Mag., vol. xv., 

 p. 396.] 



f The following is the descending arrangement given in Mr. Williams's 

 former paper: 9, floriferous slates and sandstones {culm measures); 8, Cod- 

 don Hill grits; 7. trilobite slates; 6, Wollacomb sandstones; 5, Morte 

 slates; 4, Trentishoe slates ; 3, calcareous slates of Linton ; 2, Foreland 

 orDunkerry sandstone; 1, Cannington Park limestone. 



