52 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 16, 



island, namely from Ryde to Culver Cliff, from Shanklin to Fresh- 

 water Bay, and from the Needles to Yarmouth, showed that there are 

 no traces there of the Lower Erratic Tertiaries or Boulder Clay. 

 There is, however, abundance of flint-gravel, having much of the 

 aspect of the Upper Erratics ; and a deposit answering to the warp- 

 drift, which has been described in former commimications as spread 

 in other districts over the denuded surface of that and of older for- 

 mations, and mainly influencing the variations of soil. 



Part of the undercliff at Ventnor consists of a mass of partially 

 water-worn chalk and chalk-marl, enveloping and covered by flint- 

 gravel, closely resembling some of that which occurs similarly asso- 

 ciated in the Cromer Cliffs. It has evidently slipped from a con- 

 siderable height in the cliffs which overhang the town. 



Flint-gravel only slightly water-worn occurs, in its greatest deve- 

 lopment, on the summits of the lower range of hills throughout the 

 island. A mass of it, at least 60 feet thick, caps Headon Hill ; and 

 a considerable thickness of it may be seen on the high ground in 

 the neighbourhood of Osborne. The same kind of gravel, more 

 water-worn, and evidently formed during the denudation of the ori- 

 ginal deposit, is found in lower situations associated with a loamy 

 warp-drift, which frequently attains a depth of 5 and 6 feet ; both 

 deposits following the contours of the denuded surface on which they 

 rest. Similar phaenomena occur on the opposite coasts of Hamp- 

 shire and Dorsetshire. 



In the absence of organic remains from the gravel, and until the 

 Upper Erratics of Norfolk, Suffolk, and Essex, whose age is defined by 

 the presence of the Norwich Crag, shall have been traced further south- 

 ward, so that their identity with the flint-gravel can be proved or dis- 

 proved, its age may admit of a question*. This however is certain, 

 that at whatever period the gravel may have been formed, and at 

 whatever period denuded, the loamy deposit, called the warp-drift, is 

 of very recent origin, and was not formed till after the denuded sur- 

 face on which it rests had existed some time under subaerial con- 

 ditions. 



The evidence on which this conclusion is founded is similar to that 

 presented by the pit at Gaytonthorpe in Norfolk, and is exhibited at 

 the base of Headon Hill in Tolland's Bay. On the summit of the 

 cliff, which is about 60 feet high, marl and calcareous tufa, abounding 

 with land shells of existing species, are developed beneath the warp- 

 drift. These calcareous deposits extend for about 300 yards from 

 the base of Headon Hill. Near the N.E. termination there is the 

 section which is given on the opposite page. 



The warp-drift which covers these calcareous deposits consists of a 

 brown sandy loam, more tenacious towards the lower part, with no 

 traces of lamination, and containing fragments of flint and of the 



* It must be borne in mind that this paper lias been locked up since the begin- 

 ning of 1848 in the archives of tlie Government Geological Suney. In recent 

 communications to the Society, I have been altle to speak more confidently of the 

 age of this gravel ; see Table, Quart. Journ. Geol. Soc. vol. ix. p. 295. 



