1850.] AUSTEN — SANDS AND GRAVELS OF FARRINGDON. 475 



after such disturbance such area should still continue to belong to 

 the deep-sea zone, would not necessarily be productive of any very 

 distinct geological features, such as that of want of conformity ; and 

 the only evidence of such change might be in mineral character, or 

 even in the colour of the deposit, as in the case between the upper 

 marls of the new red sandstone series and the lower marls of the lias. 

 In this instance the whole series, from one to the other, is presented 

 in our own southern counties as a consecutive one, and it is only in 

 places where the physical disturbance produced a very different set 

 of conditions over given areas, that the long lapse of time and the 

 succession of changes in animal life are recorded, which really sepa- 

 rate the new red sandstone group from the liassic. 



The change which separates our lower greensand from the gault, 

 over the Wealden district, is viewed as merely a change of mineral 

 character; but the transition is everywhere so abrupt^, as to 

 signify that a vast amount of physico-geographical change marks 

 the separation ; and it is this feature of change which corresponds 

 with the broader line of separation indicated at Farringdon between 

 the gault and the beds next below it, and shows that the continuity 

 of the two deposits is only apparent, or, in other words, that with 

 reference to their physical conditions, they are independent groups. 

 Nor is this independence less strongly marked with respect to the 

 fossil fauna of the neocomian, as compared with that of the gault and 

 upper greensand deposits f. This fact was clearly established as to the 

 portion of the neocomian which occurs in the Isle of Wight, by the 

 joint work of levels, and determination of species, of Prof. Edward 

 Forbes and Mr. Ibbetson, and is asserted most broadly with refer- 

 ence to the neocomian of France by M. d'Orbigny ; but whilst the 

 upper part of the neocomian is thus dissevered from the gault, the 

 line of separation does not seem to be equally broadly drawn between 

 its lower beds and the oolites. In Switzerland, as at Villengin, and 

 along the course of the Leyne, whence the tjrpe of the " lower neo- 

 comian" was first taken, there appears to be a perfect continuity 

 from the group of strata representing the Portland and Kimmeridge 

 beds into those containing Spatangus retusus, Lamk. We have already 

 seen the extent to which very competent observers in this country 

 have traced out an agreement between the oolitic and neocomian 

 forms. Prof. Phillips speaks decisively as to the mixture of Kim- 

 meridge and cretaceous species in the beds of Speeton and Knapton ; 

 and at the Meeting of the French Geologists at Boulogne, certain 

 reputed cretaceous forms are stated to have been found in the Port- 

 land beds, such as Corbis corrugataXi Sow. sp. 



* In point of fact, the gault here has been deposited on an uneven surface of 

 lower greensand. 



f Of the molluscous fauna of the so-called lower greensand of the S.E. of 

 England, not a single species passes up into the gault. 



X Nor is this the only locality where the reputed lower beds of the cretaceous 

 series would seem to belong rather to the oolitic. After describing a section at 

 Saulxce-aux-Bois, M. d'Archiac observes, ** On voit qu'ici il y a eu une sorte d'os- 

 cillation entre les derniers sedimens jurassiques, et les premieres couches creta- 

 cees." — Groupe Moyen de la Form. Cret. p. 283. 



VOL. VI. — PART I. 2 L 



