404 



PEOCEEDINGS OF THE GEOLOGICAL SOCLETT. [Mar. 21, 



instance, where a large quantity is washed and run in troughs, as is 

 frequently necessary in the cement- works and brick-fields of North 

 Kent, it is found that the amount of sand left varies considerably in 

 different locahties. At the cement- works about one mile and a haK 

 south-west of Eochester it is very large ; near Sittiugbourne, on the 

 other hand, it is comparatively small. (The former is near the junc- 

 tion of the Upper and Lower Chalk, the latter near the top of the 

 highest chalk of that part of the country.) 



Mr. Prestwich* has speculated on the origin of the green colour. 

 I would add one note. It seems to occur where carbonate of lime 

 has been dissolved. We find it, as noticed above, on the decomposed 

 surface of Kmestones ; and where lines of greensand or sandy clay 

 occur in the Lower Tertiaries, there we most often find casts of shells f. 



The chief deduction from these observations is, however, general — • 

 viz., that we cannot safely draw any conclusion as to the conformability 

 or unconformabihty of a porous formation upon a limestone from an 

 examination of the line of junction only, since that may be- very 

 much modified after the deposition of the newer formation. 



The unconformity may be inferred from other evidence, as, for 

 instance, in the case of the Thanet Sand, which, it is well known, is 

 not the direct successor of the highest Cretaceous strata found in 

 England. 



4. On the " Lower Loi^-don- Teetiaeies " of Kent. By William 

 Whitaker, Esq., B.A. (Lend.), E.G.S., of the Geological Survey 

 of Great Britain. 



[Plate XXII.] 



Contents. 



1. Introduction. 



2. Thanet Beds. 



3. Woolwich and Reading Beds. 



4. Oldliaven Beds, 



5. General relations of the Divisions 



of the "Lower London Ter- 

 tiaries " to one another. 



Fossils. 



On the Outliers of Sand on the 

 North Downs, which have 

 been classed with the Crag. 



Conclusion. 



Description of Plate XXII. 



§ 1. Inteoductiox. 



The follomng paper is meant to give some of the results of the 

 Geological Survey work in the Tertiary District of Kent, and to lay 

 before the Society the conclusions to which that work has led me, in 

 order that they may receive that criticism which is so valuable to 

 every observer. 



I give results only, so as not to burden the Society with a descrip- 

 tion of sections, which would be out of place here for two reasons : 

 — first, because Mr. Prestwich has already described the chief sec- 

 tions of the district, and I can therefore refer to his well-known 



* Quart. Journ. Gaol. Soc. vol. x. p. 244. 



t Perhaps the carbonate of lime neutrahzes the effect of the acidulated water, 

 and prevents its acting on the silicate of iron. 



