472 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Junel9, 



view iu the simple form in wliicli it is here stated ; what I would 

 urge is the great importance, in a physical point of -^dew, of the 

 distinct independence of the Farringdon series of deposits, and their 

 total separation from the cretaceous, as parts of a consecutively de- 

 posited group, by the interrention of a yast period of denudation. 



The process of denudation of any mass of sedimentary deposits to 

 a giyen depth is probably equally slow, or implies an equal space 

 of time with that which was required for its accumulation ; and it 

 imphes too a complete change in the relation of the mass of water 

 (the same agent in both cases) to the sea-bed. No broader lines can 

 possibly be drawn by which to separate masses of old sea-beds, than 

 those which indicate so great an amount of physical change as this ; 

 and bearing always in mind that geology is nothing more than the 

 physical geography of former periods, we must allow to such features 

 a primary importance beyond that of the continuity or first appear- 

 ance of certain specific organic forms : the changes in the suites of 

 such forms, through a series of deposits, are nothing but the conse- 

 quences of new conditions brought about by the ceaseless oscillations 

 of the earth's surface. 



Haying established, on physical considerations, the complete sepa- 

 ration existing between the Farringdon deposits and those of the 

 nearest portions of the true cretaceous series, it remains for us to 

 inquire into the amount of fossil forms which may serye to connect 

 them. The fossiliferous locahties of the Farringdon beds are Rowde, 

 Seend, Calne, and Farringdon : the recorded species are to be found 

 in the * Mineral Conchology,' in the lists of the ' Geology of Cony- 

 beare and Phillips,' in those of Dr. Fitton, prepared by Mr. Lons- 

 dale and Mr. Sowerby, and in Mr. Morris's Catalogue. 



In the Table of Species a column is added for the '^gault and 

 upper greensand," for the purpose of comparison with a portion of 

 the true cretaceous series of this country. The numerous physical 

 considerations we haye gone oyer will hdweyer preclude the possibility 

 of the Farringdon sands being grouped with the gault, eyen did the 

 two accumulations present some amount of agreement m their famias ; 

 the gault, moreoyer, is not an independent formation, but merely the 

 accumulation of a giyen condition of deep sea, synchronous as a 

 whole with that portion of the cretaceous deposits which we call 

 " upper greensand.'^ 



