82 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 21, 



That this 290 feet is composed of a threefold series of strata, the 

 lowest of which reposes on the Plastic Clay. 



That each division of the series commences with a zone of pehhles, 

 and passes upwards from stiff clays to sandy clays and sands *. 



Of the lowest series nothing is known with certainty, except its 

 thickness (100 feet) and the mineral composition of its strata, as 

 shown in the Deep-Well boring. 



Of the middle series, which includes a thickness of 134 feet, a 

 large portion has been seen in open cuttings on the Works. It in- 

 cludes in its upper part the "Argillaceous sands with Dentalium" 

 and the " Sands with Lingula,^^ described above. The shell-rock in 

 the " Sands with Lingida " at the top of this series probably repre- 

 sents the Bognor Rock of Sussex ; but of this I cannot speak with 

 certainty, as I have no evidence of the height of the Bognor Rock it- 

 self above the Plastic Clay. 



The upper series, having a thickness of from 50 to 60 feet of clays 

 and sandy clays, including the " Clays with Cyprina ,^^ has been suffi- 

 ciently described above. There can be no doubt whatever that these 

 last beds represent the upper beds of the so-called London Clay of the 

 Alum-Bay and Whitecliff sections. It is evident that the whole 

 of the strata above described are included in group 3 and part of 

 group 4 of Mr. Prestwich's Section of the Whitecliff strata. 



The accompanying Sections (fig. 3), which are drawn strictly to 

 measure, exhibit a comparison of the Lower Eocene strata of Ports- 

 mouth, with the already well-known Section at Whitecliff Bay, 

 and may, I hope, be ultimately useful for comparison with a much- 

 to-be-desired well-section at Bognor. 



I have not thought it necessary to compare the Portsmouth Lower- 

 Eocene strata with those of the London basin, such comparison 

 in effect having been already made bv Mr. Prestwich so long since 

 as 1847. 



Gravel- and Mud-Deposits resting on the Lower Eocene Strata. 



The superficial deposits seen in the excavations at Portsmouth 

 deserve a short description, if only on account of the fine sections 

 exposed. 



The first or oldest of these deposits is the gravel-bed shown in the 

 Section (fig. 1) as capping the higher portion of the ground. The 

 base of this gravel-bed stands at from 15 to 20 feet above low-water 

 level, and rests on the unequally eroded surface of the clay. It is 

 a light-coloured subangular flint-gravel, and probably represents 

 the " white gravel " lately described by Mr. Codrington f. The 

 ground on which it rests forms a low escarpment facing to the 1^. and 

 N.N.E., the direction of the escarpment coinciding with the outcrop 

 and line of strike of the upper beds of the " Clay with(7?/prma." 



A few patches of contorted gravel containing large, partly rounded 

 flints, have been exposed at a slightly lower level near the edge of 



* A like sequence in the mineral character of the Lower aila Middle Eocene 

 deposits in the Isle of Wight has heen noted and commented on by Mr. Fisher 

 {vide Quart. Journ. Geol. See. vol. xviii. p. 65). 



t Quart. Journ. Greol. Soc. vol. xxvi. p. 535. 



