1856.] BOUE DOVER STRAITS. 325 



sloping obliquely from the umbo to the posterior border ; the mar- 

 ginal fold of this side is slightly flattened, on which a series of con- 

 centric ridges are seen crossing the lines of growth at different angles ; 

 the umbones are small and placed near the centre ; the surface is 

 only marked with delicate lines of growth. 



Length 2^ inches. Breadth 1|-|- inch. Thickness 1^^ inch. 



Affinities and differences. — This shell resembles C. IcevigatuMy 

 Lye, in the smoothness of its surface, bat is distinguished from it by 

 the shortness of its posterior side, and the band of concentric ridges 

 which extends from the umbones to the posterior border. 



Local and stratigraphical position. — Collected only from the 

 Cephalopoda-bed of Frocester Hill. The species is dedicated to my 

 friend Edward Hull, Esq., F.G.S., of the Geological Survey. 



Cardixjm Oppelti, Wright, nov. sp. 



Shell smooth, convex, slightly inequilateral ; umbones large, pro- 

 minent, incurved, nearly central ; anterior side rounded ; posterior 

 side slightly produced and gently truncated ; on this more or less 

 angular band numerous concentric ridges are seen. 



Length 2 inches. Breadth 1^ inch. Thickness 1^ inch. 



Affinities and differences. — This shell resembles C. Icevigatum, 

 Lye, but it is a more elongated and compressed form : the posterior 

 side is flattened and ornamented with concentric ridges which are 

 absent in all the specimens of C. Icevigatum which I have examined. 

 It may prove to be only a variety of that Inferior Oolite shell when 

 a larger number of specimens permit a more rigorous determination 

 to be made. 



Locality and stratigraphical position. — Collected from the base 

 of the Sands at Nailsworth, where it is not common. The species is 

 dedicated to my friend Dr. Oppel, of Stuttgart, well known for his 

 extensive acquaintance with continental Oolitic Geology, and author 

 of " Die Juraformation Englands, Frankreichs, und des siidwestlichen 

 Deutschlands." 



4. On the Probable Origin of the English Channel by means of 

 a Fissure. By M. Ami Boue, For. Mem. G.S. 



[Abstract.] 



The author, having met with a published proposal to construct a 

 submarine tunnel across the Straits of Dover, pointed out that it was 

 highly probable that the English Channel had not been excavated 

 solely by water-action, but owed its origin to one of the lines of dis- 

 turbance which have fissured this portion of the earth's crust ; and 

 that, taking this view of the case, the fissure probably still exists, 

 being merely filled with comparatively loose material, and would 

 prove a serious obstacle to any attempt to drive a submarine tunnel 

 which would have to traverse it. 



