240 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



A stronger break, physically, takes place between the '* Lits Co- 

 quilliers " and the " Glauconie grossiere " than is shown at the base 

 of the " Lits Coquilliers ;" but nevertheless, that break seems of less 

 importance with reference to the animal life of the period, as so con- 

 siderable a proportion of the species of the ** Lits Coquilliers " are 

 continued up into the Glauconie grossiere and Calcaire grossier*. 



We cannot expect to find in each country an exact identity in 

 the fossils of these various geological zones. The difference is often 

 important. In each centre there are a considerable number of 

 species peculiar to it ; and at the same time that there are usually 

 a suificient number to establish the correlation of the strata, there 

 yet remain sufficient diiferences to show the variations produced by 

 habitat, depth of water, temperature, &c., such as would exist over 

 areas of like extent in the present day. These variations, while they 

 afford matter for speculation as to what was the ancient distribution 

 of land and water in these districts, yet leave resemblances suffi- 

 ciently strong to enable us to engage in such speculations upon a sure 

 and certain basis. They also show us that whilst it may not be safe to 

 expect, upon any a priori reasoning, a repetition of a like order of 

 palseoutological succession in the two countries, we may nevertheless 

 often successfully seek for that order by taking into consideration the 

 limits within which the differences may, under any circumstances, 

 be admitted to extend ; and, having determined and ehminated the 

 phsenomena which may be considered aberrant, we may look for like 

 terms of comparison where the conditions again become more general 

 and common. 



Fragmentary as our Tertiary deposits appear to be, I believe this 

 to be in a great measure the effect of denudation and local peculiari- 

 ties of structure, and that we shall eventually be able to connect 

 many of them over large areas, and to show that they are for the 

 most part merely the littoral and shallow water deposits of seas 

 which probably had a wide and oceanic range. 



* At the same time, although I group the Lower Bagshot Sands and their 

 equivalents in the French series, with the Paris rather than with the London 

 Tertiaries, in consequence of their apparently closer relationship, both palae- 

 ontologically and lithologically, with the former thaa with the latter group, 

 still that relationship is not so close but that those deposits may prove to be 

 entitled to a separate grouping. For the zoological gap between the London 

 Clay and the Bracklesham Sands and Calcaire grossier is such, there not being 

 10 per cent, of species in common, as to indicate a length of time of considerable 

 importance. This period may be probably only in part represented by the 

 Lower Bagshot Sands and Glauconie moyenne. The fauna of the " Lits Coquil- 

 liers " is, after all, very distinct, not only from that of the beds beneath 

 them, but also, although to a less extent, from that of the Calcaire grossier 

 above. In England, where mineral evidence alone assists us, it is difficult to 

 separate the two groups ; in Belgium, both in mineral character and in the 

 few organic remains, there is still less apparent distinction, whilst in the Paris 

 area, where organic remains become numerous, their individuality as forming 

 a distinct fauna becomes far more marked. From the facts given by M. Alcide 

 d'Orbigny, it seems probable that this deposit attains still greater importance and 

 distinctiveness as it ranges southward. It is in this series that the great develop- 

 ment of Nummulites takes place within the London and Paris areas. The under 

 lying London Tertiaries are as much marked by the absence of these Foraminifera 

 as the " Lits Coquilliers " are by their extraordinary abundance. 



