274 PEOF. J. PEESTWICH ON THE EAISED 



(11) Portsea. — This is tlie farthest point westward to which these 

 boulders have been traced, though pebbles of the old and crystalline 

 rocks are to be found beyond, but these are such as could have 

 been drifted by tidal action along a shore-line, whereas the boulders 

 are evidently ice-borne. Mr. Codrington describes the boulders at 

 Portsea as " rounded and smoothed," " from 1 to 2 cubic feet in 

 size," and consisting of " granite, syenite, and greenstone, as well 

 as of sarsenstone."^ When I visited the pits none were visible, ^o 

 mention is made of beach-shells. 



(12) The Isle of Wight.— There is a Raised Beach, thick, but of 

 small extent, at Bembridge Point, whence it extends at intervals '^ 

 to near Eyde. It consists of a mass of rolled chalk-flints, some 

 Tertiary tiints, and white quartz -pebbles, rounded fragments of 

 ironstone, cherty ragstone, and sarsenstone, with a few large 

 pebbles of light-coloured and red quartzite, and small pebbles of 

 lydianstone and slaty hornstone, in a matrix of quartzose sand 

 roughly bedded. No large boulders and no shells have been found. 

 The beach is overlain by 20 to 30 feet of Head, composed of brick-^ 

 earth with a small proportion of angular local debris. In this 

 Kubble-drift Mr. Codrington found an ovoid flint-implement perfectly 

 sharp at the edges. ^ 



With the exception of this bed at Bembridge, the fragment at 

 Portsdown Hill,* and uncertain indications near Pool, the Beach 

 is now lost sight of for the remainder of the Hampshire coast, and 

 is not met with again until the Isle of Portland is reached. (In my 

 former estimate of the altitude of Portsdown Beach an observation 

 by aneroid barometer led me to fix it at 125 feet above sea-level, 

 but the Ordnance Survey shows that it is under 100 feet.) 



Nevertheless, it is probable that the Beach passed round the back 

 of the island, rat no great distance from the present shore. The 

 extensive landslips at the extreme southern points have obliterated 

 all the older coast features, but between Blackgang Chine and 

 Preshwater Gate they remain intacc. Along this line a continuous 

 low cliff (80 to 150 feet) fronts south, while at a short distance 

 northward the central Chalk range of the island runs east and west. 

 On the top of this cliff is a bed of gravel (and brick-earth) from 5 to 

 10 feet thick. In the absence of any rivers flowing off or tnrough 

 the Chalk range on this part of the coast, this gravel was referred 

 by Mr. Codrington to a river which is supposed to have flowed 

 at the back of the island between the present shore and a land 

 to the southward, now removed, and then to have passed through 

 Preshwater Gate^ northward into an old Solent river. This sup- 

 position, however, involves difficulties similar to those which attend 

 the Solent-river hypothesis. The gravel is wanting in the essential 

 characters of a fluviatile gravel, the gradients are incompatible 



^ Quart, Journ. Geo!. Soc. vol. xxvi. (1870) p. 535. 

 ^ Bristow, Mem. Geol. Siirv. ' Isle of Wight,' p. 102. 

 ^ Quart. Journ. Geol. Soc. vol. xxvi. (1870) p. 542. 

 * Ibid. vol. xxviii. (1872) p. 38. 

 ' Ibid. vol. xxvi. (1870) p. 540. 



