1852.] PRESTWICH ON THE THANET SANDS. 263 



soft impressions, and varying in thickness from about 15 to 20 feet. 

 Beneath them is a nearly continuous, tabular, light grey, hard, con- 

 cretionary, calcareous sandstone, 1 to 2 feet thick, with few fossils, but 

 often covered with large vermiform casts. Next follows 4 to 6 feet 

 of hght-coloured argillaceous sands with a few fossils. Below this 

 a darkish grey semi-indurated clayey sand crops out, and is well ex- 

 posed between high and low water mark. It abounds in characteristic 

 and well-preserved fossils of the Thanet sands, by far the most abundant 

 shell being the Cyprina Morrisii. This stratum forms the base of the 

 cliff nearly to the Reculvers, and is throughout marked by the same 

 fossils : at the same time, the top bed of the Thanet sands, which at first 

 contains only a few shells, becomes more fossihferous, and near 

 there abounds in well-preserved but very friable shells, chiefly the 

 C. Morrisii, together with the Cucullaa crassatina, Thracia oblata, and 

 many others comparatively rare (see list, p. 248). The cliff ends at the 

 Reculvers ; the marsh-lands separating this spot from the Isle of Thanet 

 then intervene; at Birchington the cliff rises again, but consists of 

 chalk without any capping of tertiary strata. The relation, however, 

 of the Thanet sands to the chalk was shown by a well dug at the 

 Reculvers some few years since. 1 was informed that the chalk was 

 reached at the depth of about 70 feet, after traversing sands which 

 became more clayey in descending, and with shells in patches through- 

 out. This position of the chalk is shown on the left of the section. 



Sect. 4. Just below Upnor the hills approach close to the left bank of the Medway, 

 and the numerous pits opened for ballast-sand exhibit some good sec- 

 tions of the lower tertiaries. (For a description of Stratum " 3," see paper 

 before cited. Quart. Journ. Geol. Soc. vol. vi. p. 263.) The middle 

 group " 4 " is considerably expanded, and consists almost entirely of 

 sands ; the upper bed is fossiiiferous and of a light yellow colour, and 

 the lower bed is of a very light tinge of yellowish green, with subor- 

 dinate beds of small flint-pebbles, but without fossils. Between these 

 two sands are a few feet of dark grey laminated clays and sands, full of 

 Cyrena cuneiformis, Melania inquinata, and some other fresh or brack- 

 ish water shells. The Thanet sands rise from beneath the sands " 4 *' 

 at the pit (at b) just behind Upnor village, but the characters of the 

 two groups are here so much alike, that it is not easy at first to distin- 

 guish them apart, especially as neither contain fossils. They may then 

 be traced at intervals along the river-bank, by Upnor Castle, to a chalk- 

 pit on the foot-road to Stroud, where the lowest beds are seen reposing 

 on the chalk, with the usual green-coated flints at their base. They are 

 here much mixed with fine greensand, and are also without fossils. The 

 dip at Upnor is about 3° N.E. 



Sect. 5. This is a well-known locality and has been frequently described, chiefly 

 however with reference to the upper beds, which abound in the so-called 

 Woolwich shells. (For particidars of this section and its fossils I beg 

 to refer to Dr. Buckland's paper. Trans. Geol. Soc. vol. iv. p. 284, and 

 to the Rev. Mr. De la Condamine's paper in the Quart. Journ. Geol. 

 Soc. vol. vi. p. 440.) The Thanet sands are here fine-grained, siliceous, 

 and without organic remains, if we except traces of plants (hi fragment- 

 ary casts and impressions), and the cast of the Pholadomya mentioned 

 by Mr. Morris (see text, p. 265). The upper part of these sands are 

 nearly white, very loose, and almost purely quartzose ; in descending 

 they become tinged ash-grey and yellow, and mixed vnth a small pro- 

 portion of argillaceous matter, and wdth a perceptible quantity of green- 

 sand in their lower part. The basement-bed as usual is an impure 

 greensand, with green-coated flints, and is only reached occasionally 

 on the floor of the pit. The view here given is one at right angles to 

 the road, and was exposed a few years since ; this part of the pit is not 

 now worked, and the sands are almost entirely sloped over. The pre- 

 sent works are just round the end of this section. The Basement Bed 

 of the London Clay is given with a query, as I am not yet sure whether 



