THE PLEISIOCENE DEPOSITS OF THE SUSSEX COAST. 353 



new section at Medmerry most of the large detached boulders had 

 been found to belong to igneous, granitoid, or gneissic rocks, with 

 a certain admixture of hard Eocene sandstone. This peculiar as- 

 semblage had always puzzled me, for I could not understand how 

 shore-ice could bring various rocks from the Channel Islands or 

 other more distant localities without bringing anything from the 

 Isle of Wight. It now appears, however, that the granitoid rocks 

 are in a small minority, and that the bulk of the material comes 

 from the Isle of Wight and the Sussex coast ; but the Isle of Wight 

 rocks being either calcareous or else much jointed, the boulders fell 

 to pieces through the action of frost, or w^ere crushed into moderate- 

 sized fragments, and these are soon destro3'ed when once dislodged. 



It would appear that every previous observer had been able to 

 examine only the erratics loose on the • shore, or re-deposited in 

 various parts of the strata overlying the gravel. This would account 

 for nothing but hard rocks being contained in the list published by 

 Godwin-Austen, and would also explain the mistake in his diagram- 

 section, which placed the erratic deposit above instead of below the 

 marine bed with Pecten polymorphus. As I shall show farther on, 

 re-deposited erratics of moderate size are particularly abundant in 

 the mud-bed directly overlying clay with Chiton siculus. The oc- 

 currence of blocks at this level probably misled Godwin-Austen as 

 to the true succession. 



The discovery of a striated erratic fifty miles south of the nearest 

 glacial deposits in the Thames Yalley deserves comment. ^ The 

 block was a large mass of Bognor Eock, measuring 5x4 feet and 

 probably weighing upwards of 2 tons. It w^as full of Fectimculus 

 hrevirostris and Valuta denudata^ but as it lay with the smooth face 

 embedded in the Bracklesham Clay, the striae were not at once 

 observed, and the piece figured on the opposite page was broken oif and 

 taken as a characteristic fragment of a known Eocene rock. Only 

 on unpacking and washing the specimen, after my return to London, 

 were the striae noticed, so that it is impossible to say whether the 

 whole of the buried surface of the erratic was grooved in the same way. 

 The striae probably were formed whilst the rock was still part of 

 the solid projecting ledge that yet exists off Bognor. A ledge of this 

 sort in an icy sea would form an obstacle to the drift-ice, which swept 

 backward and forward with every change of tide and wind. The 

 surface would thus tend to become irregularly scored and striated, and 

 occasionally, through the formation of packs, the ledge would be 

 shattered and pieces carried away. The striated erratic found at 

 Selsey must not be taken as evidence of the occurrence of glaciers 

 on the shores of the English Channel, for everything points to the 

 agency of shore-ice and frost alone. 



^ Eamsay, in a note on p. 85 of the 'Catalogue of the Tertiary and Post- 

 Tertiary Fossils in the Museum of Practical Geology,' mentions the occurrence 

 of ice-scratched stones at Selsey. The account given by Ramsay, both in the 

 ' Catalogue' and elsewhere, seems, however, to be taken from Godwin-Austen, 

 who speaks of boulders ' presenting beautifully smooth and polished surfaces,' 

 alluding evidently to the action of the sea and not of ice. The chalk-flints 

 placed by Ramsay in the rock-collection at Jermyn Street are not striated. 



