250 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 21, 



shell of the " Terrain Landenien." The P. margaritacea is also mentioned by 

 Nyst as a fossil of the " Terrain Landenien," and by D'Archiac and Melleville as 

 from the " Sables Inferieurs." 

 (m.) Resembles the Saxicava Grignonensis of Deshayes. 



We have therefore in the Thanet Sands 39 species of Testacea, of 

 which 24 are determined. Of these only 6 are common to the whole of 

 the Eocene series, and 2 more range as high as the London Clay. 

 Of the remaining 1 6 peculiar to the Lower Tertiary strata^ 3 extend 

 into the " Basement-bed " of the London Clay, and 2 to the level 

 of the Woolwich group, whilst as many as 1 1, or nearly one half of 

 the whole, are peculiar to the Thanet Sands. The distinction is not to 

 be attributed to different conditions of the waters, for although at 

 Woolwich this has necessarily operated by excluding the more marine 

 species and introducing in their place others of fluviatile and sestuarine 

 origin, still in, and adjoining, the Isle of Thanet, both the middle and 

 upper divisions of the Lower London Tertiaries are marine, and con- 

 sequently the conditions in this respect of the three groups are equal, 

 and still the difference of fauna holds good. 



Annexed are the detailed sections of the two localities where the Thanet Sands 

 are most fossiUferous (the Reculvers excepted). Their relation to the other parts 

 of the Lower London Tertiaries is shown in sections 1, 2, & 3, PI. XV. 



Fig. 4. — Section of part of the Cliff at Pegwell Bay, near 

 Ramsgate. {s in Section 1, PL XV.) 



cdci 



Feet. 



1. Drift of light-coloured brick-earth, with a thin irregular seam of gravel 



(angular and small round flints), mixed with broken fragments of the 

 shells of the underlying beds, at its base 4-6 



2. Light yellow slightly clayey sand with shells in layers and patches ; *' a," 



tabular masses of fissile micaceous calcareous sandstone, with few 

 shells, — a very small Corhula often occurs in great abundance ; " b" 

 small calcareous concretions, in which the Pholadomya Koninckii is not 

 uncommon ; " c," large concretionary blocks, often very argillaceous ; 

 their lower surface frequently presents masses of shells, especially the 

 Cyprina Morrisii. Traces of Plants occur both in ** b " and " c." 16 



3. Grey clayey sands, rather dark when wet, but lighter-coloured when diy 



(the upper part especially looking at a distance almost like chalk), — the 

 lower part is more argillaceous and darker ; " d*' a seam of grey clay 

 with shells in patches ; *' e," a thin layer of impure greensand full of 

 very friable shells. Several shells, especially the Pholadomya cuneata, a 

 Nucula, and the small Cytherea, together with frequent traces of plants, 

 are dispersed in some abundance and in a good state of preservation 

 throughout this bed, "3" 15 



