1852.] 



PRESTWICH ON THE THANET SANDS. 



251 



Fig. 5. — Section of the Sand-pit hy the side of the Railway at 

 Richborough Castle^ near Sandwich. 



SI 



09 S 



rcJ O 



Feet. 

 1. Light brownish-yellow clayey sand with a few very scarce and not 



determinable bivalve shells 3 



^2. Very sandy light brownish-grey clay full of small, rough, twig- 

 like fragments or pieces of iron sandstone, with cores of yellow 

 sand, and having the appearance of vegetable origin, — contains 

 a very few and very small black flint-pebbles 2^ 



Very light and loose ash-green sand, rather fine, — in some places 

 coarser, with one thin seam of shells {Corbula, Glycimeris, 

 and Cyprind). The lower part contains an occasionally ochreous 

 layer. A few small round flint-pebbles are dispersed throughout. 

 The lower part of this stratum has taken up part of the under- 

 lying bed, and the line of separation is, therefore, not very sharply 

 marked 8 



Rather bright ochreous clayey sand, passing down into alight brown- 

 ish yellow colour, in some parts with seams of sandy clay. Casts of 

 shells are common in this bed, but more particularly in the lower 

 and more argillaceous part of it 7 



Light yellow loamy sand with shells in irregular layers and patches 

 on the left hand of section. They are very abundant — in some 

 places in fragments, in other places whole and perfect, but ex- # 

 tremely friable 4 



Beyond this a bed of hard semi-indurated sand, 3 feet thick, with a few shells, 

 rises. Argillaceous beds, not well exhibited, succeed. 



The surface on the top of this section consists of about 1 foot of earth, with a 

 few pebbles, chiefly the rounded ones. The hill rises at the back about 10 feet 

 higher, but no section is exposed. Small round flint-pebbles are numerous on the 

 surface of the hill. 



4. Conclusion. 



From the facts brought forward in the preceding pages, but which, 

 with regard to the middle division of the Lower London Tertiaries, 

 will be described more in full hereafter, it appears that while this 

 latter group exhibits on the same horizon, a fauna at one place 

 marine, at another sestuarine, and at last passing into one chiefly 

 fluviatile, the Thanet Sands maintain within the same area a uniform 

 marine character. In its range westward the fossils are certainly few, 

 but still the occurrence of the Pholadomya, which is never found in 

 the Woolwich clays and conglomerates, or in the sands interstratiiied 

 with the mottled clays, but is, as before mentioned, met with in the 

 sands beneath the shelly fluviatile beds at Woolwich and Charlton, 

 afl'ords an unmistakeable proof of the different conditions under which 

 the two divisions were formed. Taking therefore these facts, in 

 conjunction with the persistent lithological character of the lower 



