418 Dr. Fitton on the Strata, S^c. 



The best stone is that of the " Pol-lids"\ or concretions between the 

 upper-head and the race; and the masses are fre(|ucnlly l)Iuish within, 

 but cream-coloured on the outs.de. The blocks after being raised 

 from the pits, are spread out on the surface, and exposed to the effects 

 of frost; which splits, or renders them easily divisible, into flags or 

 " slate," — the fissures being parallel to the general stratification of the 

 country. 



The doubts which Mr. Prevost has expressed on the relations of 

 the strata at Tilgate forest in Sussex, have been adverted to by 

 JVIr. Mantell, who has mentioned the chief distinctions between 

 that remarkable deposit and the Stoncsfield beds.* In fact, no 

 point in the Geology of England is at present better determined, 

 than the existence of a numerous and varied series of strata be- 

 tween those groups. 'J'he Tilgate grit it is true resembles that of 

 Stoncsfield, in its concretional form and its connexion with sand; 

 but it contains not a particle of oolite ; — and grit of the same 

 mineralogical character occurs not only in several other parts of 

 the Ilastings-sands, but occasionally throughout the Weald clay, 

 thus pervading a series of strata decidedly different from the oolite 

 in geological site : while the presence of freshwater shells at Til- 

 gate, those of Stoncsfield being marine, aff'ords a Zoological cha- 

 racter not less distinctive. 



I remain, my dear Sir, 



Very truly yours, 



Wm. Henry Fitton. 

 W. J. Broderip, Esq. 



* " Remarks on the geolofrical position of the Strata in Tilpjate Forest, 

 Sussex." Jameson's Edinb. Pliilos, Joiirn. April to Dec. 1826, p. 162.— See 

 also a Notice by Mr. Mantell, Geol. Trans. 2d Series, I. p. 131. 



