240 Mr. H. Seeley on the Stratigraphical Position 



Species. 



Peculiar to the Chalk 7 



„ „ Upper Greensand 12 



„ Gault 2 



„ „ deposit 10 or II 



Common to the Chalk and Upper Greensand 9 



„ „ Upper Greensand and Gault 6 



„ „ Chalk, Upper Greensand, and Gault . 10 



Ranging to the Chalk 26 



„ „ Upper Greensand 39 



„ Gault 18 



From this Table, the probability of the bed being Gault is 

 seen to be so small that it may safely be dismissed, since out of 

 the species ranging to other strata but 8 occur in the Gault. 

 Nor is the probability strong in favour of it being Chalk, since 

 there is, besides the fact of a greater number of species actually 

 existing in the Greensand than in the Chalk, the difficulty of 

 supposing that, in this district alone, Gault fossils would have 

 lived on to the Chalk sea. But if the bed is admitted to be 

 Greensand, there will be 27 species occurring in that formation 

 to weigh against 16 ranging to the Chalk. This, when the 

 chalky nature of the deposit and other conditions already men- 

 tioned are taken into consideration, must go far towards deter- 

 mining the question. Granting, then, that the Red Limestone 

 is one of the newer members of the Greensand, and adding the 

 10 species peculiar to the red bed, there will be 37 Greensand 

 species to compare with 16 of the Chalk ; or, limiting the com- 

 parison to peculiar species, thei-e would be 22 of the former to 

 balance against 7 of the latter. And when it is remembered 

 that more than two-thirds of the fossils of some deposits in- 

 dubitably Greensand have never occurred in that formation pre- 

 viously, and when we bear in mind the evidence from strati- 

 graphical position, little further evidence will be needed to place 

 the Hunst'on Limestone in that Cretaceous zone. 



As already remarked, the Tourtia presents the nearest ana- 

 logue. Very few species are common to the two beds ; but the 

 palseontological conditions are essentially the same ; many of the 

 fossils are those of the Chalk, a majority occur in the Upper 

 Greensand, and some in the Gault. The proportions are not 

 very dissimilar. The Tourtia is admitted to be a member of the 

 Upper Greensand. And thus the Red Limestone may also be 

 referred to Greensand on evidence as good as that which proves 

 the identity of distantly situated Tertiary deposits. Judging 

 from some of the fossils, it is not impossible that when the 

 Speeton Clay shall be carefully investigated, its upper part will 

 prove to be of Gault age, if not newer *. Should it be so, the 



* For in the middle of the formation is a bed containing Rostellaria 



