Dr. FiTTON on the Strata below the Chalk. 3S3 



4. The occurrence of oolite containing freshwater shells, near the bottom of the Purbeck strata 

 at Combe Wood (144.), p. 275-6, is another fact deserving of notice, and may perhaps explain 

 some doubtful appearances in the uppermost bed of the Portland Series (the Roche) ; which, 

 although full of marine petrifactions, and commonly oolitic, has very much the aspect of fresh- 

 water limestone. It can easily be imagined that the bank, or land, consisting of the Portland 

 strata, when first raised above the sea, was covered with marine remains, which might subse- 

 quently have been cemented together, at the bottom of a freshwater lake. 



5. The existence of pisolitic (or granular) oxide of iron, in the Wealden, is probably not con- 

 fined to the coast near Hastings, where I found it to be generally diffused; p. 166. The fact of its 

 occurrence in this formation is the more deserving of notice, from the great abundance of that ore 

 in the marine deposits supposed to be contemporaneous with our Wealden, in other parts of Eu- 

 rope : supra, (168.) p. 330. 



(171.) Similarity of Deposits of different Epochs. — The mineralogical 

 resemblance between some of the strata above and beneath the Wealden, 

 is very remarkable. — The upper part of the Portland formation in the Vale 

 of Wardour is so like chalk, that it bears that name in some of the quarries; 

 and both there and upon the coast of Dorsetshire it contains flint nodules, 

 not distinguishable from those of the chalk. — The Portland sand abounding- 

 in green particles, cannot, in itself, be distinguished from the green-sands 

 above the chalk, nor from those below ; the green matter in all is of the 

 same nature; the calcareous concretions are like those of the "Kentish- 

 rag" : yet the deposition of these groups was separated by intervals 

 of time sufficient, in the first two cases, for the accumulation of all the 

 Wealden strata, and in the two latter, for that of the chalk. — The strong re- 

 semblance of the variegated sands and marl of the Wealden to those of the 

 new red sandstone, and of both to the tea-coloured and variegated marls of 

 the beds above the chalk in the Isle of Wight, has been already mentioned. 

 — The Wealden, again, has many striking points of resemblance to the coal 

 measures. The shale, sandstones, and clay iron-stone of the latter are not 

 distinguishable from those of the Hastings-sands, which are, in fact, a coal 

 formation : and in addition to the Unios and other freshwater shells long 

 known in the coal formations, the recent discovery of Cypris, in freshwater 

 limestone, among the coal measures in Scotland*, is another point of agree- 

 ment. 



These resemblances, of which other examples might easily be given, in de- 

 posits separated by great intervals of time, demonstrate the identity of the 

 processes which are still going on with those of the more ancient epochs, 



* See, however, upon this subject, the remark of Mr. Sowerby, as to the possible resemblance 

 of the fossil crusts of the marine genus Cytherina, to those of Cypris : Appendix, p. 345, under 

 the head Cypris Valdemis. 



