1852.] PRESTWICH ON THE THANET SANDS. 261 



species, the prevalence of Cyprina, Astarte, Glycimeris, and Thracia 

 in these strata, combined with the absence of such genera as Pyrula, 

 Cancellaria, Valuta, Conus, Mitra, and Pleurotoma, of the numerous 

 large Cephalopods, and other animal and vegetable products of a pre- 

 sumed warmer climate, which abound in the London Clay, rather tend 

 to point out the probability of a lower temperature in the sea of the 

 Thanet Sands, — a fact in unison with the physical evidence of a sea 

 open apparently to the north, and an island presenting a barrier to 

 the south, and extending probably from the central portion of the 

 present Weald to near the eastern borders of France. By itself this 

 circumstance would not be entitled to much weight, but as it has 

 been shown that the physical conditions under which such a result is 

 possible, are in themselves probable, we may not unreasonably view 

 them to a certain extent in the relation of cause and effect, and con- 

 sider that the probabilities in favour of both are increased by the 

 corroborative testimony thus afforded. 



EXPLANATION OF PLATE XV. 



The following sections show the dimensions and position of the Thanet Sands 

 at intervals in their range from east to west, — from the point where they are best 

 marked to that near to which they disappear heneath the London Clay. After a 

 range of a few miles further west, they thin out altogether (fig. 3, p. 236). In 

 soft strata of this description the pit-sections are rarely permanent, although there 

 are some which are at present good and illustrative. The sections, therefore, 

 selected to serve as types are those which appear most permanent, two of them 

 being coast- sections and not liable to any very great change, and the others being 

 works opened to supply a constant demand and likely to continue to be worked for 

 many years. All the sections are actual ones, except that of Woodnesborough Hill, 

 which is planned from surface-outcrops and wells, and is introduced to show the 

 relation of the sands at Richborough to the outcrop of the Chalk, and the probable 

 thickness of the Thanet Sands. The same observation applies to a small portion 

 in the middle of the Upnor section No. 4. 



Sect. 1. Gives a view of the end of the Isle of Thanet cUfFs adjoining the valley 

 of the Stour. Pegwell Bay is about two miles west from Ramsgate. 

 Chffs of chalk only are continuous round the other parts of the so-called 

 island. At the point a in section, a remnant, 3 to 4 feet thick, of the 

 basement bed of the Thanet sands, with the usual layer of green-coated 

 flints, reposes upon the chalk. Between that point and b the chff is 

 a good deal obscured by debris and the slopes made for the road which 

 descends to the beach; and at 6, where the section can again be 

 resumed, the cliflF is composed entirely of the tertiary sands and drift, 

 so that the junction of the chalk with this mass of Thanet sands is not 

 seen. From the dip of the strata at a, the high level there of the small 

 portion of Thanet sands, and the position of the main mass at b, it is 

 probable that a fault occurs between these two spots ; I have not, how- 

 ever, seen it exposed. 



From b to the cliff end at c the section is continuous, and shows per- 

 fectly well probably all the series of the Thanet sands except the very 

 highest and lowest beds. The lowest part, towards b, consists of about 

 10 feet of light-coloured, grey, and greenish clayey sands with traces of 

 Plants and of a Ditrupa or Dentalium, and, continuing in the direction 

 of c, pass up into 12 feet of more argillaceous and greener beds, then 

 into ] feet of laminated darkish grey sandy clay with a few fossils, 

 succeeded by 8 feet of grey clayey sand, drying white, and with nume- 

 rous small fossils. This is overlaid by 15 feet of dark clayey laminated 



