344 Prof. Sedgwick on the Classification of the Strata [M ay, 



4. Shanklin sand (ferrugino-green-sand of Mr. Webster). The 

 three preceding of marine origin, and very nearly related to 

 each other. 6. Weald clay. 6. Hastings sands. The two pre- 

 ceding, with a very peculiar suite of organic remains, chiefly of 

 freshwater origin. 7. Purbeck limestone : in zoological charac- 

 ters approaching the two preceding; but in mineralogical cha- 

 racter more nearly associated with No. 8. 8. Portland oolite. 

 9. Kimmeridge clay. 10. Coral-rag ooUte. 



With what part of the preceding series shall we then identify 

 the clay of the vale of Pickering ? To answer this question cor- 

 rectly, it is obviously necessary to determine the physical cha- 

 racters and the organic remains of the formation. Unfortunately 

 the sections on the coast, disguised by enormous accumulations 

 of diluvium, give us much less information than might have been 

 anticipated. I may, however, venture to assert, that the fossils 

 of the argillaceous cliff which succeeds the chalk are not identi- 

 cal with the suite of the Cambridge gait; and that some speci- 

 mens which I found in situ, and others derived from the same 

 locality, which I have seen in private collections, are identical 

 with a part of the fossils of the Kimmeridge clay in the neigh- 

 bourhood of Weymouth. The general agreement of the Kim- 

 meridge and Pickering clays is further confirmed by the near 

 agreement of their mineralogical characters, and by the beds of 

 bituminous shale which are subordinate to both of them. 



Allowing, however, that a portion of the Pickering clay is the 

 true representative of the Kimmeridge clay, it may still be asked, 

 whether the upper part of it may not represent some of the other 

 beds between No. 1 and No. 9 of the general series aboveraen- 

 tioned. As far as regards the immediate vicinity of the coast, 

 I am disposed to answer the question in the negative, for the 

 following reasons : 1. There are, 1 believe, no traces of the 

 Portland and Purbeck beds north of the Humber.* 2. The 

 Weald clay and the Hastings sands seem to constitute a local 

 deposit confined to the south-eastern parts of England ; and 

 being principally of freshwater origin, cannot in any way be 

 co-extensive with the marine formations which are above them 



in the Annuls nf Philosophy for 1822), I made sonie remarks on Mr. Greenough's 

 geological map,'wliich I take this opportunity of correcting. At that time I was unac- 

 quaiiued with the coasts of Kent and Sussex, and confounded the Kentish rag (which I 

 only knew by description") with the green-sand rock of the UnderclifF in the Isle of 

 Wi^ht. I now tliink that on any geological map of an ordinary size, it would not be 

 expedient to subdivide the colours further than has been done already; and that the 

 green-sand, the Cambridge gait, and the Shanklin sands, might be conveniently repre- 

 sented by one colour with a designation applying to the whole group. This appears to 

 have been very nearly the system of Mr. Greenough. 



• If this assertion be true, it by no means follows that the same formations are want- 

 ing on the west side of the wolds of Lincolnshire. A correct description of the beds 

 between the chalk and great oolite in that county is at present a desideratum wliich, we 

 may hope, will be soon supplied by some of the members of the philosophical societies in 

 the north of England, 



