44(5 PROCEEDINGS OF THE eEOLOGICAL SOCIETT. [Maj 24^ 



3. River-gravel and brick-earth (Loess). 



1. Suhaerial Beds*. — Under this head we class those beds which 

 are formed by rain before it has collected into streams. 



In our area they are of two kinds — 



(1.) Eainwash-briekearth and chalky wash. 



(2.) Unstratified flint gravel and beds of angular chert. 



(1.) The action of the weather is always degrading rocks, and the 

 matter thus detached is carried down the hill-sides by rain. In some 

 places this accumulates to a considerable thickness, and may then be 

 conveniently termed "rainwash." When carried down into the streams 

 it goes to form true alluvial deposits, or is carried away to sea. 



It is frequently diificult to distinguish between rainwash-brick- 

 earth, and true alluvial loam. Both may contain land-shells, and 

 the former is sometimes roughly stratified, but rarely, if ever, so 

 distinctly as the latter. 



(2.) Beds of chemical origin left as the result of the chemical action 

 of rain on the strata come under this head. The " dry valleys " of 

 the Chalk have usually a considerable thickness of flints in their 

 lowest parts. These flints are entire, or, if broken, are sharply 

 fractured by weather, never rounded or water- worn. These vaUeys 

 are probably due to the dissolving away of the Chalk along lines 

 of underground drainagef. Deposits of flints also occur frequently 

 on the top of the chalk downs, mostly mixed with clay (clay-with- 

 flints) ; and this clay, too, is in most cases probably the residue of the 

 chalk which has been dissolved awayj. 



The beds of unstratified flint gravel that are met with in many 

 places on the Lower Greensand, Gault, and lower slopes of the Chalk 

 are probably the residue left, as the Chalk escarpment was gradually 

 worn back by subaerial denudation. This gravel may be seen on 

 Pennenden Heath, near Maidstone, for instance ; it differs entirely 

 from the river-gravel by its want of stratification, and by the absence 

 of Wealden pebbles ; and it consists of angular and subangular 

 flints, with occasionally a few Tertiary pebbles, the interstices of the 

 gravel being often filled up with clay. This gravel is sometimes very 

 chalky, as is the case at a place about a mile N.E. of Aylesford, 

 where the deposit is 15 feet thick and rests on the Gault. 



2. Modern Alluvium. — The modern alluvium does not differ in 

 any important respect from that of other rivers, and does not need 

 any very particular description. It consists of loam and gravel. 

 About Tunbridge and Talding the alluvium forms broad meadows ; 

 between Yalding and Teston it gets quite narrow, and then disap- 

 pears altogether until you have passed Maidstone. At Aylesford allu- 

 vial meadows are once more met with, forming a broad plain near 

 Snodland. 



3. River-gravel and Brick-earth (Loess). — E,iver-gravel§ occurs 



* See Godwin-Austen, Quart. Journ. Geol. Soe. vol. vii. p. 1851, 118. 



t Whitaker, ' Mem. Geol. Survey,' Sheet 7, 1864, p. 96. 



J Ibid. Sheet 7, pp. 63, 66, and Sheet 13, 1861, pp. 54, 55. 



§ We have used the term " river-gravel " instead of " valley-gravel," in order 

 to prevent the gravel of tn\e river-origin from being confounded with the sub- 

 aerial gravel which also occurs in the Medway valley. 



