44 Mr. Webstet's Reply to Dr. Fitton. [Jan. 



Those of the gault and the Folkstone marl are numerous and 

 identical, while in the Isle of Wight they are extremely few. 

 Mr. Smith has named this bed sometimes the Oak tree clay, and 

 sometimes he calls it Brick earth. He describes it in his work 

 on Organized Fossils, published in 1817, p. 36, as existing at 

 Godstone ; to the north of Reigate, under the Reigate stone; at 

 Leighton Beaudesert, Bedfordshire ; at Grimston, in Norfolk ; 

 and at Westering, in Bedford, four miles SW of Ampthill. It 

 is in all these places distinguished bv its characteristic fossil, the 

 siball fusiform belenmite, and contains many other fossils of 

 this bed, as hamites, inocerami, depressed ammonites, &c. This 

 blue marl is identified by Smith with the Tetsworth clay, not- 

 withstanding the latter has been considered to be the weald clay 

 bv Prof. Buckland, in his table of the order of the strata. The 

 brick earth mentioned by Townsend above the red sand at 

 Devizes is probahlv this bed, and I have little doubt but that it 

 may be traced all round the west side of the chalk as Smith has 

 represented it in his map. 



From the above considerations, I am still inclined to think, 

 that the bed extending through Coxheath, Nattield, 8cc, belongs 

 to the fernigiiiotis sand of former geologists, and not to their 

 green sand. 



With respect to the ferruginous sand be/ow the weald clay, 

 the Hastings beds, we have nothing satisfactory to prove that it 

 exists on the west of the chalk. It has not been stated any 

 where (as far as I know), that the ferruginous sands in Bedford- 

 shire contain any fossil shells, or this question might be decided, 

 since the fossils of the Hastings beds are peculiar, and sup- 

 posed by some to be chiefly, if not entirely, of freshwater origin, 

 whereas those of the Nutheld ranee are marine. Nevertheless, 

 it may yet be found in that quarter, although we have no evi- 

 dence before us from which we can draw any conclusion ; and 

 it is quite surprising to iind, that, at a time when some imagine 

 the geological account of England to be nearly complete, we 

 should be absolutely in want of materials for determining so 

 important a question. 



Having now arrived at a certain point in this discussion, viz. 

 the determina'^ion of what were the original g;fe« and Jh'iugi nous 

 sands, and having stated my reasons lor oiving these names to 

 the beds in the Isle of Wight, and in the wealds of Surrey, Kent, 

 and Sussex, it is natural that I should inquire how it could be that 

 the bed which I imao:ine to be /he f'cii iigi/ioiis so/zf/ of Smith, came 

 to be called the trite green sand by IMr. Conybeare, and several 

 other oeologists of the present day. I think I perceive the solu- 

 tion of this in Mr. Conybeare's work itself, the " Outlines." He 

 begins his exauiiuation of the beds below the chalk at Folkstone ; 

 and finding there a dark coloured argillaceous bed immediately 

 below the chalk, -he calls it (though inaccurately) the chalk marl, 



