PRESTWTCH FOSSILIFEROUS IRONSANDS, N. DOWNS. 331 



surface of that island was formed of a larger tract of Lower Green- 

 sand and Chalk (with Tertiary cappings) than was exposed in the 

 former island, and that the detritus from this island, worn down by 

 coast- and river-action, contributed the chief supply in forming the 

 encircling deposit of Crag*. 



The great denudation of the Weald is thus brought to a still more 

 recent date than this period, these Crag beds extending to the very 

 edge of the chalk-escarpment and having been truncated by the same 

 action that wore down that escarpment. I have previously shown 

 that this operation had taken place at a comparatively recent period, 

 as some beds of drift were cut off in the same way ; but I was unable 

 then to assign a date to that drift, some of which now appears how- 

 ever to be older than this Crag. We may conclude, therefore, that 

 the final denudation of the Weald took place subsequently to the 

 Crag period. At the same time, as, in the Suffolk area, a great 

 break takes place between the Coralline and Red Crags, the lower 

 one being a deposit formed in tranquil waters, whereas the Red 

 Crag contains debris worn and broken from other beds, and reposes 

 upon a strongly abraded and indented surface of the Coralline 

 Crag, it seems not improbable that another elevation of the Wealden 

 area took place between the Coralline Crag and Red Crag periods, 

 whereby the boundaries of the island f before referred to were so 

 extended as to form a continuous barrier between the French and 

 English Crag areas at or soon after the Red Crag period. This 

 would be in harmony with the fact so often noticed, that at the period 

 of the Red Crag we first find northern shells prevailing to an extent 

 that leads us to believe that the sea of that Crag period was open to 

 and connected with the northern seas, aud would show how the 

 communication which at the period of the Coralline Crag existed 

 with more southern seas was then cut off and ceased. 



Note. — Since the above paper was read I have again visited all 

 the localities named therein, but without finding any better sections. 

 It is evident that it is on the chalk -downs between Folkestone and 

 Wye that these beds are best developed, and T would especially direct 

 attention to Paddlesworth and to the neighbourhood of Kingmill 

 Down, as well as to the hills above Otford and thence to Vigo Hill. 

 A considerable number of fresh specimens have been obtained from 



* On the chalk-hills between Upper Gatton and Great Shabden, and about a 

 mile and a quarter in a direct line N.N.W. from Merstham, there is an outlier of 

 light yellow sand, a small section of which may be seen in a pit in the fir-wood 

 on the east of the road. This sand differs in several respects from the Lower Ter- 

 tiary sands, and yet is not like any of the presumed Crag beds we have described. 

 Its base is not shown, and only a patch of gravel overlies it, nor could I find any 

 fossils. I am nevertheless inclined to place it with the Lenham group, for it is 

 coarser and not so worn as the Lower Tertiary sands ; it contains also a few thin 

 flakes of ironstone, some flint-pebbles (white and not so well worn as the Eocene 

 pebbles), bits of unrolled flints, also some patches of quartzose grit, and a few rare 

 and small fragments apparently of the chert and ragstone of the Lower Green- 

 sand. A deeper excavation might possibly expose some of the ironstone-bands 

 and conglomerates, blocks of which are so common at Aldersted Farm on the 

 other side of the valley along which the Brighton road passes. 



f Bringing that island into connexion with the continental area. 

 VOL. XIV. PART I. Z 



