153 On some of the Strata in the Neiglibourlwod of London. 



It is in this chalk that the genus Ammonites is first met 

 with; or, in other words, it appears ihat the water which 

 formed this stratum \va- that in which this genus last ex- 

 isted, no traces oF it having been seen in the soft chalk or 

 in the other superior strata. The chief, aud perhaps the 

 only circular species of this genus which has been found in 

 this stratum, is of a large size, with nodular projections on 

 its sides, towards the back, which is generally flat. This 

 fossil appears to be of a diflerent species from ativ of those 

 that are found in the subjacent strata. 



It is very remarkable th U in this stratum, the last in which 

 the genus aminoiiiles is niel with, so remarkable a deviation 

 from the ongtjial form of the genus should occur, as almost 

 lo claim its being considered as the characteristic of another 

 genus. In the lossil here leferred to, which possesses all 

 the other characters o\ am77ionile.s, the spiral coil is disposed 

 in a forrn rather approaching to that of the oval than the 

 circle*. 



In another fossil of this stratum, a still more extraordinary 

 deviation exists. This fossil possesses the concamerations 

 and the foliaceous sutures of the cornu ammonis; but, in- 

 stead of being spirally coiled, it has its ends turned to- 

 wards each other, so'ncwhat in the iorm of a canoe. This 

 peculiar rorm has led to the placing of this fossil under a 

 sejjarate genus, which has been named Scaph'tcf. 



Of the extent of this stratum no correct account has 

 been given; but there is snfTicient reason lor believing that 

 it accompanies the other chalk in its range through this 

 island. It also appears that its peculiar fossils exist in it 

 at very considerable distatices. Thus ihb oval ammonite, 

 which is found in the Sussex hills, likewise occurs in the 

 hard chalk of Wiltshire; and the scap/i/'/t^y, another inha- 

 bitant of the Sussex hills, has also been discovered in Dor- 

 setshire. 



On comparing the precedins; sketch with the Essay on^ 

 the Mineralogieal Geography of the Neighbourhood of Paris, 

 bv Messrs. Cuvierand Bron^mart, son)c important variations 

 will be perceived between the strata found above the chalk 

 in this island and in France. In France, the strata above 

 the chalk difil-r both in number and quality from those 

 which have been hitherto observed in a similar situ.uion in 

 England. In France, loo, several strata of siuid and sand- 

 stone exist above the strata of the gravel formation, which 

 in this island aj^pear to be highest. 



* Organic Remaius, vol. iii. pi. ix. fi^.f). f IbiJ.vl iii. p! x%!0All. 



The 



