8 PBOCEBDIlSrGS OF THE GEOLOGICAL SOCIETY. [NoV. 9, 



and the Nore ought to form but a subordinate proportion of the 

 constituent material, while in the Canterbury-heights gravel nearly 

 as much subcretaceous material as flint ought to occur. The case 

 of the East-Essex gravel, especially of that part of it which extends 

 from the Nore to Eochester, is a very strong one ; for the chalk forms 

 but a very small part of the area drained by the Medway, and, while 

 the gravel-producing material, the flint, constitutes only a small per- 

 centage of any given amount of chalk strata removed, especially of 

 the Lower Chalk which obtains in this area, the portion of the Lower 

 Greensand formation which is drained by the Medway is largely 

 made up of beds of hard stone. The Hastings-Sand formation, too, 

 abounds with indestructible gravel-forming material, and in as large 

 a ratio at least as does the chalk. Omitting the Weald Clay and the 

 Gault as non-gravel-forming strata, we have, roughly speaking, the 

 following proportions borne by the areas of those gravel-producing 

 formations lying beyond the East-Essex gravel termination at 

 Eochester whose drainage falls into the Medway, viz. : — 



Lower London Tertiaries 0-25 



Chalk 1-00 



Lower Greensand 2*75 



Hastings Sand 3*00 



Total 7-00 



"While the chalk thus figures for only one-seventh in area, it would, 

 in proportion to any given quantity of strata^ removed, yield no more, 

 indeed less, of flint than the Lower-Greensand beds, or even the Hast- 

 ings-Sand formation, would of hard gravel- forming material. 



If it be objected that the stone beds of the Lower Greensand are 

 mostly limestone, and therefore soluble under the action of acidulated 

 water, such objection does not apply to the Hastings-Sand material, 

 of which, indeed, the broad sheet spreading over the Weald-Clay bot- 

 tom is mainly, and in some parts exclusively, composed. Neither 

 has it prevented the gravels of the Lower Greensand country from 

 being principally made up of the stone beds of this formation. 

 Moreover, the Kentish Lower-Greensand Limestone, so extensively 

 used in building, is not of a perishable nature, and much of it is in 

 that broken condition most suitable for supplying fragments for 

 gravel-accumulation; while on the other hand so perishable a 

 material as the Kentish Chalk has, according to Messrs. Topley and 

 Foster, found its way, in the form of nodules, into gravels near 

 Maidstone. Allowing, therefore, the fullest weight to this objection, 

 can we resist the admission that if the East-Essex gravel, especially 

 that part of it lying between Eochester and the Nore, resulted from 

 the transport of the Medway, the flint debris in it (exclusive of the 

 Lower Tertiary pebbles) should be largely outbalanced by subcreta- 

 ceous material, instead, as the case is, of that material forming but 

 a very small proportion of this gravel ? This iuference wiU not be 

 appreciably weakened hj supposing that the respective escarpments 

 extended southwards in former time, because a careful examination of 



