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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NOV. 20, 



a single species is found not now known in a living state, nearer than 

 Egypt. There is nothing more remarkable in a Cyrena of the Nile 

 being associated with the molluscs of the present Thames at Clacton, 

 than there is in the association at Brentford of the same shells with 

 the hippopotamus and the rein-deer. 



If, again, over these fluviatile deposits of the valley of the Thames, 

 we find beds of gravel and loam destitute of organic remains, and 

 extending beyond the limits of the fluviatile deposits to the high 

 grounds, their thickness varying with the elevation and form of sur- 

 face, we have a counterpart to the erratic warp of Norfolk, traceable 

 over the higher and lower grounds, deepening in the latter, and co- 

 vering, at Gaytonthorpe, freshwater and mammalian deposits which 

 fill hollows in the denuded surface of the erratic tertiaries (see figs. 1 

 & 2, p. 28). 



Such I believe to be the facts of the case ; but they can only be 

 considered as partially established, until the superficial deposits of the 

 valley of the Thames from its source to its mouth shall have been 

 mapped, and their relations to the deposits of the glacial sea in 

 Norfolk, Suffolk, and Essex shall have been satisfactorily determined. 

 I know of no other mode of solving the question i than by laying down 

 the variations in the deposits of that sea, with the same attention 

 which has been bestowed on the older sea beds, which have hitherto 

 been exclusively honoured with a place on geological maps. 



In the present communication I propose to show, that the soils 

 which cover the chalk of Kent at various heights are analogous to the 

 erratic warp of Norfolk ; that they are the result of aqueous transport ; 

 and not, according to the prevalent assumption, produced by atmo- 

 spheric erosion which during the lapse of ages dissolved and removed 

 the calcareous matter of the chalk, leaving behind, as upon a filter, its 

 fine siliceous and argillaceous particles and its flints. 



The district to which these remarks apply, comprises only a few 

 square miles lying a little to the S. of Dartford ; but, if of limited 

 extent, it is a fair type of the Kentish Chalk district in general. The 

 rapid changes of soil in this district, where ferruginous and non-cal- 

 careous clay, clay-loam, and loam more or less sandy, as well as white 

 calcareous soils, may be seen in the space of forty or fifty acres, would 

 be a strong presumption against the hypothesis of formation, in situ, 

 by chemical solution, unless it can be shown that the composition of 

 the subjacent chalk varies with the variations of soil ; and unless a 

 satisfactory explanation can be offered of the solution of the calcareous 

 matter in one case, and its non-solution in another. I shall furnish, 

 however, positive evidence of aqueous transport, in alternation of 

 deposit. 



The village of Hartley stands on an elevated table-land of chalk, 

 covered, to depths varying between one and four feet, by a soil of non- 

 calcareous clay-loam passing into a sandy loam, and changing from 

 one to the other within very short distances. The surface is thickly 

 strewn with large unabraded flints and some rounded flint pebbles, re- 

 ferable to the eocene tertiaries, of which there are some outliers a little 

 to the northward, as for instance at the village of Darenth. The 



