456 INFERIOR OOLITE AMMONITES. 



more usually seas similar to the English Channel or the North Sea. One other 

 point has yet to be noticed, namely, they were so fossilised that we now find the 

 geographical ranges of certain species, of certain genera, and even of certain 

 sub-orders of Ammonoidea to be very restricted ; thus certain forms which are 

 common in Southern Europe are rarely found in England, and other forms which 

 are scarce in the former area are not found at all in the latter. 1 



Such being the facts of fossilisation, the question at issue is whether, after all, 

 the larger number of Ammonites may not have been preserved in the immediate 

 vicinity of where they lived. It may be granted that many of the shells were 

 dispersed after death, only to be broken to atoms on the nearest beaches, and 

 that some of them escaped this fate because they never reached the beaches. It 

 has always been allowed in regard to worn specimens, and those occurring with 

 extreme rarity in beds contemporaneous with rich Ammonitiferous deposits of 

 other districts, that dispersal after death was the easiest explanation of their 

 presence in such cases. In regard to excellently preserved specimens accummu- 

 lated in large numbers over certain definite geographical areas the case seems to 

 be different. Universal distribution after death would tend to produce damaged 

 specimens, — would, on the whole, lead to greater uniformity of occurrence, — and 

 would produce a greater uniformity of geographical ranges than is found to be 

 the fact. 



It will be seen from the above remarks that Dr. Walther's conclusions as 

 summarised in ' Natural Science ' (loc . cit. y p. 246) require to be accepted with 

 reservation. " The distribution of Cephalopod-shells provided with air-chambers 

 bears no relation to the habits of the living animal." It must bear some relation, 

 though perhaps not a direct one ; but the distribution would be different if 

 Ammonites were pelagic from what it would if they lived in shallow water a few 

 miles from a shore ; and it might be different according to their shape. " The 

 richness of a deposit in chambered Cephalopod-shells does not depend on the 

 distribution or habits of the living animals." It would depend upon it unless 

 universal dispersal after death had taken place. Given localities rich and poor 

 in living Ammonites, a dispersal after death of 25 per cent, or more would still 

 leave their relative richness unaffected. " The distribution of chambered Cepha- 

 lopod-shells bears no relation to the changing character of the containing rock, 

 or to the depth of the sea in which it was deposited." Yet it may be objected 

 that Ammonites are found more abundantly in somewhat shallow-water deposits, 

 and that they, in common with other molluscs, would seem to have avoided 

 localities where a large amount of sediment was being collected. 



1 See p. 452 ; also " Jurassic Ammonites," ' Geol. Mag.,' dec. 4, vol, i, No. 3G1, p. 298, July, 

 1894. 



