1852.] PRESTWICH ON THE THANET SANDS. 259 



Again, we find in the next or middle division of the Lower London 

 Tertiaries an enormous accumulation of round flint-pebbles, which, 

 generally speaking, could not have been rolled and worn into their 

 present shape on the spots in which they are now found. They were, 

 I believe, formed during the deposition of the Thanet Sands, and after- 

 wards spread out by other operations on the surface of these sands 

 and incorporated with the strata formed during the period of the 

 Woolwich and Mottled Clay series which immediately followed. 



From the foregoing considerations it is probable that there was 

 some extent of dry land, possibly an island, somewhere intermediate 

 between a line drawn on the north from Farnham towards Canter- 

 bury, and on the south between Winchester and Newhaven, and 

 extending eastward into the north of France * ; and that the long- 

 continued wear on its coast accumulated on the shores extensive 

 banks of pebbles, whilst the finer sediment produced at the same 

 time, in conjunction with the debris brought down by the operation 

 of streams, formed at a distance from the land the strata of this 

 oldest Eocene epoch f . Diagram fig. 8 illustrates this hypothetical 

 view. 



One reason for beheving that this land formed an island is, that had 

 the land stretched far east and west it must have reached beyond the 

 chalk-district, and it is more than probable that the currents and tides 

 of the sea would then have drifted the shore-pebbles from the older 

 rocks in one of these directions, and mixed them up with those derived 

 from the flints of the chalk, along some parts at all events of the Une 

 of coast ; whereas in an island the clifl's of which consisted exclusively 

 of chalk or of soft beds of greensand (if without drift-gravel), the 

 flints would form the only material capable of resisting long wear and 

 of furnishing the beach-shingle J. On this view alone can I account 



* In his memoir " Sur TEtendue du Systeme Tertiaire inferieure " in the north 

 of France, M. Elie de Beaumont arrives also at the same conclusion respecting the 

 existence of an island in the position of the present Wealden and Boulonnais during 

 the formation of the Lower Tertiaries period, and gives a sketch of the geography 

 of that period. (Mem. Soc. Geol. de France, vol. i. p. Ill, and pi. 7. fig. 5.) 



t The extent of this land, however, I believe to have been small compared with 

 that of the period of the Woolwich fluviatile and aestuarine deposits, for all the 

 remains of plants are in a very fragmentary state and not in any mass, as though 

 large rivers were wanting and the land were drained merely by small streams and 

 torrents ; in confirmation of which view it is to be observed also that there are no 

 distinct river-deposits with fluviatile shells in the Thanet sands, which fact shows 

 that the materials were either derived from the wear of the coast or from small 

 streams which would not efifect the uniformity of character of the marine deposit. 

 This might require an immense period of time, but of this we have evidence in those 

 really wonderful accumulations of rounded flint-pebbles before mentioned. Further, 

 we know that the Thanet sands are spread much more widely over the chalk than 

 are the fluviatile series, in consequence probably of a further elevation of the land 

 and the conversion into dry land of part of the adjacent sea-bottom at the latter 

 period. 



t There is, I am aware, some difficulty in determining the origin of these round 

 flint-pebbles. They are evidently chalk-flints, but they present some characters 

 rather distinct from those of the ordinary chalk-flints of the neighbourhood of 

 London. The fossils found in them are very scarce and not very conclusive. 

 Mr. Flower, who has examined with great care large numbers of these peb- 

 bles, considers them derived from some more distant locality, as their organisms 



