1868.] JL'I)D — SrEETOX CLAY. 223 



believe, taking into consideration the number of faunas which it re- 

 presents, in wiportance also, to the English Lias. 



IV.' Is THE Speexon Clay the Equivalent of the Gault? 



Before entering upon the detailed description of the various strata 

 composing the Speeton Clay, which is the principal object of this 

 paper, I propose to reexamine the evidence on which some of them 

 been referred to the age of the Gault. 



The recognition of the important fact that the fauna of the upper 

 part of this formation had Cretaceous rather than Oolitic affinities 

 is due to Professor John Phillips, and is a great step in advance of 

 any previous attempt at the correlation of these beds. When we 

 consider the crude condition of the sciences of Geology and I'alaeon- 

 tology at the date of the publication of ' The Geology of Yorkshire,' 

 we shall be struck in this, as in so many other instances in the same 

 remarkable work, with the success of its bold generalizations ; and, 

 remembering that the very existence- of the typical Neocomian fauna 

 was not pointed out by MM. MontmoUin* and Thurmannf until 

 six years later, we shall be satisfied that any nearer approximation 

 to the determination of the real age of the Speeton Clay was at that 

 time impossible. Unfortunately the reference of this formation to 

 the Gault, which was at the first little more than a suggestion on the 

 part of the author, and which has ever since been regarded by him 

 as doubtful, has been too frequently treated by others as if conclu- 

 sively established. 



Besides the direct palaeontological evidence on this subject, there 

 is an a priori argument, deducible from the stratigraphical relations 

 of the beds, which I think is entitled to considerable weight. The 

 Hunstanton limestone (Red Chalk) has now yielded an abundant and 

 well-marked series of fossils, which enables us to refer it to its 

 true position in the geological scale. Now I am but expressing 

 the conviction of all palaeontologists who have examined the 

 subject of late years when I say that this bed cannot be of later 

 age than the Upper Greensand, and may be of as earli/ age as the 

 Gault. But between this bed and the Speeton Clay we have, 

 as Professor Philhps himself has so well shownj, an enormous 

 unconformity, certainly one of the greatest and most striking which 

 occurs in this country. On the supposition that the Speeton Clay or 

 any part of it is of the age of the Gault, we are driven to the con- 

 clusion that this remarkable unconformity exists either between the 

 Upper Greensand and the Gault, or in the midst of the Gault itself 

 — a conclusion, I need hardly say, not o^ly altogether at variance 

 with what we know of the stratigraphical relations of these beds, 

 both in this and other countries, but also directly opposed to what 

 we might expect from a comparison of their faunas ; for, as has 



* " Memoire sur le terrain cretace du Jura," Mem. de la Soc. des Sc. Nat. 

 de Neuchatel, vol. i. p. 49 (1836). 



t Bull, de la Soc. Geol. de France, vol. ix. p. 46 (1837). 



+ Vide Map of Yorkshire ; also ' Geology of Yorkshire " and Quart. Journ. 

 Geol. Soc. vol. xiv. p. 84 (section). 



