fitton's section at atherfield. 323 



appears to be the rule ; as will be evident by a comparison of sections, 

 — by which great variation has been proved to exist within very short 

 distances. The Kentish limestone alone shows the dissimilarity be- 

 tween the two principal English sections, and the comparative lists of 

 fossils in more distant places, with much agreement, show always 

 many differences of detail. 



And thus it is by no means impossible that repetitions of the Perna, 

 or of the Crackers' group, may be found to recur within this series of 

 strata in other countries, in different geological places from that which 

 they occupy at the base of the present section. 



Above the Crackers'' group, from No. 11 to 44 inclusive, — a thick- 

 ness of about 390 feet, — twelve new species only are added to the re- 

 siduary list of fossils : the Crioceras being of this number, a genus 

 which both originates and disappears in this division ; and Gryphcsa 

 sinuata, one of the most numerous shells, with many of its promi- 

 nent varieties, also appears here for the last time. In the group 14, 

 next above, there is a small influx of species ; five which had not 

 occurred before making their appearance here*, with twenty-nine 

 others brought up from the lower strata, twenty-seven of which 

 originate below No. 8 of the Crackers' group : and sixteen of this last- 

 mentioned number come even from the Perna bedsf Nos. 1 and 2. 



If the preceding observations be just, it can hardly be expected 

 that subdivisions founded upon the distribution of groups of fossils 

 will be generally applicable in remote places ; — a doubt which is sup- 

 ported by the examination of some new arrangements proposed by 

 high authority. The only indication of natural subdivision in the 

 upper part of the section at Atherfield appears in No. 45, in which 

 about five-and-thirty species have been found. The eye is at once 

 carried to this division of the Table, which is strongly contrasted 

 wdth the spaces above and below ; and the group is not only, in this 

 section, the apparent limit between a fossiliferous tract and what is 

 here a barren region, but agrees in position and fossils with others 

 which are prominent in Kent and Sussex. But in the lower parts 

 of this very section several other ranges of concretions exist, con- 

 taining similar masses of the same species, which in fact pervade the 

 whole of this section up to No. 45«. Among these the range of no- 

 dules 35«, about 150 feet below, is so rich, that if it were more ac- 

 cessible, and in a state of decomposition favourable to the extraction 

 of its fossils, it would rival the concretions of No. 45, at Black-Gang 

 Chine, or Horse-ledge near Shanklin. 



It is satisfactory to find that the views above expressed are borne 

 out and extended by the independent evidence derived from a larger 

 collection of specimens, and the simple stratigraphical apposition given 

 in the annexed table. But, whatever be their explanation, the facts 



* The five species which first appear in 45, and they have not been found in 

 any other stratum, are Venus caper ata, Cardium Voltzii, Trigonia al(Bformis, 

 Avicula pectinata, Turritella Dupiniana. 



t Many of the species repeated in 45, it will be observed, do not appear in the 

 intermediate strata ; but their existence there is highly probable, the less pro- 

 ductive strata ha\'ing been much less examined than the more fertile. 



