350 MR. C. EEID ON THE PLEISTOCEK-E 



general level. In this process the softer or more splintery rocks had 

 been crushed, so that they are now found with their angular frag- 

 ments slightly separated by gravel, or by fossiliferous Eocene clay. 

 The harder masses were sometimes driven into the clay (see fig. 1, 

 p. 348), so that I was obliged to cut away fossiliferous Eocene clay to 

 get out the Pleistocene erratic. It seems clear that most of these 

 pits are not hollows eroded by water, but dents made by the ice or 

 by erratics ; for the stratified Eocene clays generally become much 

 disturbed and contorted around the margin of the hole. The pits 

 filled with finer material probably mark the spots where large 

 erratics were formerly deposited, though, becoming again frozen 

 into the ice-foot, they were lifted out and transported to fresh sites. 



About a hundred of these pits were examined, and the conclusion 

 seemed irresistible that they afforded clear evidence of the agency 

 of floating ice. Drift-ice grounding on the ancient foreshore 

 dropped its burden of erratics betw-een tide-marks. Here they 

 were pressed deeper and deeper into the clay, for the rise and fall 

 of the tide at high-water piled ice upon any projecting rock, while 

 at low-water the rock was pressed down by the weight of the ice 

 till it was flush with the general surface. Often,- however, the 

 still-projecting boulder would be firmly frozen into a new ice-foot, 

 or accumulated mass of pack-ice, and would then be gently lifted 

 out of the hole at the rise of the spring-tides. It is thus that I 

 would account for the occurrence of empty pits, for they seem to 

 mark the former sites of blocks which may have shifted their 

 position several times before finally coming to rest. Perhaps some 

 of the basins were produced by the stranding, packing, and revolv- 

 ing of masses of ice during a storm, but the general appearance 

 of the section suggests fairly tranquil water in a sheltered bay. 

 No signs of furrows ploughed in the clay were observed, and the 

 ice was probably entirely in the form of flat-bottomed ice-foot, 

 which, at a spot like this, sheltered from the prevalent winds by 

 the Isle of Wight, would ground gently and would tranquilly melt 

 away without being driven violently into the shoals, as on a more 

 exposed coast. 



Besides the section opposite Medmerry Parm just described, 

 several erratics have been notice.d embedded in Eocene clay near 

 West AVittering, five miles to the north-west. The floor was at a 

 slightly higher level and was much cut into by later marine deposits ; 

 as, however, only a vertical section was visible, nothing more can be 

 said about these boulders. 



There has always been some uncertainty as to which of the far- 

 transported blocks found on the Sussex coast were genuine erratics, 

 and which had been brought in ballast, or had been derived from 

 wrecks. Every opportunity was therefore taken to obtain specimens 

 of each variety of rock found unmistakably embedded in Pleistocene 

 deposits^; the following is a list of the erratics found in the pits 

 near Medmerry, with the measurements of each block, and the 



^ I have to thank my colleague, Mr. J. J. H. Teal], F.E.S., for determining 

 the igneous and plutouic rocks. 



