PRESTWICH FOSSILIFEROUS IRONSANDS, N. DOWNS. 323 



usually been taken, to form part of it*. They are to be seen on the 

 Chalk Downs above Merstham ; I had met with them on the chalk- 

 escarpment near Otford in Kent, at Vigo Hill, again at places near 

 Maidstone, and thence, in increasing importance, to the Downs above 

 Folkestone. At the latter place, on the top of the hill on the Dover 

 road, some of the best sections (small though they are) of these strata 

 are exposed. I have not been able to trace the width of the deposit 

 for more than a mile or two. It seems confined to the higher 

 grounds. 



It is the consideration of the age and geological position of these 

 sands and iron-sandstones that forms the subject of the present in- 

 quiry. The sands are usually of a light buff-yellow or ochreous colour, 

 though occasionally greenish, siliceous, but mixed with more or less 

 clay commonly red, passing in places into small quartzose grits, and 

 generally containing subordinate seams and bands of coarse iron-sand- 

 stone, ironstone grit, and some flint, pebbles. The whole is very irre- 

 gular in its mode of occurrence, reposing upon a much-worn surface 

 of the chalk, ordinarily without any distinct stratification, or rather 

 the stratification is obliterated, the seams of ironstone being almost 

 invariably broken and fragmentary. There is, however, in all the 

 larger outliers a certain amount of regularity, a certain uniformity of 

 composition, and a distinctiveness of character, which, notwithstand- 

 ing their rubbly condition, led me to believe that they formed part of 

 some sedimentary deposit in situ, and that they were not drift-beds. 

 I was nevertheless unable, in the absence of superposition and of 

 fossils, to come to any satisfactory conclusion with regard to their 

 age ; I had, however, satisfied myself that the ironstones at least 

 were not drifted from the Lower Greensand, for on the chalk-hill 

 above Merstham I had found a few blocks of this ironstone f full of 

 chalk-jHnt--pebh\es together with some unrolled flints, and again on 

 the Folkestone chalk- cliffs. They are therefore newer than the Chalk. 

 The question then arose, to which of the Tertiary strata these iron- 

 stones belonged ; and as in East Kent there is found, under the London 

 Clay, a bed of light-yellow siliceous sand, with a subordinate bed of 



* It has even been a question whether the fragments of iron-sandstone belong- 

 ing to these beds have not been drifted from the Lower Greensand of the Wealden 

 area, Such ironstone-fragments, or " clinkers," as they are sometimes called, are 

 often found in abundance in the drift-gravel of the transverse valleys of the Chalk 

 Downs and in the Thames Valley. These I believe to be derived from the sands and 

 ironstones of the North Downs, although in mineral character they are difficult to 

 distinguish from the ironstones of the Lower Greensand. At the same time, I 

 would by no means say that all the ironstone-fragments of the Thames-valley drift 

 were derived from the North Downs. In the neighbourhood of Farnham they can 

 in fact be distinctly traced from the Lower Greensand through the valley of the 

 Wey into the Tertiary area ; again through the gorge of the Stour, of the Medway, 

 from the Wealden area to the lower levels of the Tertiary area. But I doubt 

 whether the abundant flint- and ironstone-gravel of the deep lateral vales which 

 do not traverse the downs, but commence at or near their summit ridge, and open 

 into the Tertiary area only, be not local and derived from the adjacent chalk and 

 the superincumbent ferruginous sands, and that they are not transported from 

 the Wealden area. 



f There apparently mixed with the drift ; but no section is exposed. 



