204 



Mr. Lyell on Shells of the Genus 



rock, which have been filled from above with rubbish, con- 

 sisting of angular fragments of quartzite, pieces of limestone, 

 and numerous fossil shells, the whole imbedded in a calcareous 

 matrix resembling that of the incumbent strata. The most 

 perfect fossils, together with the greater part of the Cones, 

 have been all found in this breccia filling the rents, and the 

 upper parts of the breccia unite with the lowest strata of 

 fossiliferous limestone in such a manner as to make it clear 

 that the fissures were filled before or at the time of the depo- 

 sition of the lowest strata of the limestone. The quarries in 

 which these sections are exposed have been opened, not for 

 the sake of the limestone but for the subjacent quartzite which 

 is used for making roads, and which at some points comes up 

 nearly to the surface. This quartzite, however, and the ac- 

 companying transition schist, are only found at a moderate 

 depth along a certain line from N.N.W. to S.S.E., in which 

 direction they form an underground ridge stretching for many 

 leagues beneath the platform of limestone. At the distance 

 of a few yards either east or west of this narrow ridge the 

 incumbent oolite or lias is of such thickness that the quartzose 

 stone cannot be worked with profit. 



Among the Ammonites which I collected myself in the rent 

 or in the bed immediately covering it, or which were given 

 me from this locality by M. Deslongchamps, were the follow- 

 ing, which have been examined by my friend Mr. Lonsdale, 

 of the Geological Society : — 



1 . Ammonites Walcottii, Alum shale. Phillips, Geol. Yorkshire, p. 

 164 ; Hunton, Geol. Trans., vol. v. part 1, p. 220 ; Williamson, 

 ibid., p. 242 ; Cheltenham, Murchison, Geol. Cheltenham, p. 

 17. 



2. A. corrugatus, Inferior oolite. Dundry, M. C. tab. 451 ; 

 Gloucester, Lonsdale, M.S. 



3. A. Stokesii, Inferior oolite? Bridport, M. C. tab. 191. Marl- 

 stone, coast of Yorkshire, Williamson, Geol. Trans., vol. v. part 

 1, p. 242. 



Among many others which were shown me at Caen and 

 named by M. Deslongchamps, were Ammonites planicost a and 

 A. Bucklandii, which occur in the lias in England, A.falcifer, 

 found in the alum shale near Cheltenham, and A. Strang- 

 le ay sii and A, Murchisonce, both from the inferior oolite of 

 England. Associated with these I saw a Belemnite, several 

 species of Pleurotomaria, fragments of aPentacrinite and other 

 fossils, which in the opinion of M. Deslongchamps indicates 

 that the formation constitutes either the upper member of the 

 lias, or is intermediate between the lias and the inferior oolite. 



