1825.] Mr. IVebster's Replj/ to Dr. Fitton. 41 



the Coxheath, IVutfield, and Wolmer Forest range which is 

 below the Folkstone blue marl. But as a decisive proof of this, 

 he states, that the bed below the blue marl is the Kentish rag, 

 which with hina is a different bed from the green sand.* It is 

 to be regretted, that the writings of Mr. Smith are rendered 

 obscure when describing these beds, by his considering the 

 Purbeck stone and the Kentish rag to be the same ; and he even 

 sometimes places the Portland stone in this part of the series. 

 But it does not appear that this geologist was acquainted with 

 the latter beds in situ; nor that their true place was under- 

 stood previously to my examination of these countries ; the first 

 table in which they w'ere correctly placed being that in the 

 commencement of my paper on the Freshwater Formations of the 

 Isle of Wight, vol. ii. Trans. Geol. Soc. ; and the author of the 

 review of Smith's Map (Edinb. Review, 1818, p. 32), seems to 

 have been aware of this circumstance. 



Thejej'riiginoiis sand of Smith is evidently the Coxheath and 

 Niitfield range, which he identifies with the Woburn sands ; 

 and in his map he places his Kentish rag properly m this bed, 

 although (perhaps through inadvertence) he arranges the 

 description as if it were above. 



Mr. Townsend describes the sands immediately under the 

 chalk as of three varieties, 1 . Green sand ; 2. Grey sand ; 

 3. Red sand (arena ferruginosa, Lin.) The first, or uppermost, 

 forms the vales of Pewsey and Warminster, and is a sand con- 

 taining dark green particles. The second is a calcareo- siliceous 

 sandstone, called firestone, which he considers as identical with 

 the firestone of Reigate, and the whetstone pits of Blackdown. 

 As he does not mention any clay between these two (and it is 

 remarkable that his green sand is not loider, but over lus grey 

 sand or firestone), I imagine that they form one mass, and ditfer 

 only in the quantity of green earth which they contain ; for the 

 firestone of Reigate is never quite without this ingredient, and 

 in the Isle of Wight the upper part of the Underclilf contains 

 more green earth than the lower. The occurrence of the fire- 

 stone in the green sand of the vale of Pewsey is important, for 

 nothing like this is found in the Coxheath and Nutneld ratige 

 called bv Mr. Conybeare and Dr. Fitton t /> e pee u sand. The fos- 

 sils of the vale of Pewsey, agreeing in general with what we 



* I was not orif^nally aware of this circumstance. 3Iy letters to Sir H. EnglefioUl 

 were publislicd several years before Mr. Smith's memoir ; and not having had an oppor- 

 tunity at that time of ekamining J'olkstone personally, but having heard the Folkstone 

 blue marl dtscril)ed as t!ie chalk marl, and the Folkstone rock as the green sand ; and 

 knowing from hand specimci.s that the Kentish rag is almost ido.uiial in appearance^ 

 with the rag of the UnderclifK, I imagined erroneously the Folkstone rock to be a part of 

 the same range with tiie Ueigate stone, and consequently to lie decidedly iiIidv,- my fer- 

 ruginous sand ; nor was I urideceived until by a visit which i made to Folkstone in 

 the summer of I6S2, 1 found that the Folkstone rock lay inmie<liately iii)on tlie weald 

 clay, witho\it tlic intervention of any ferruginous sand. 



