1916.] THE DEPOSITS. 371 



period of their geological history that they were ground down 

 to their present heights. 



The enormous pressure exerted bv the ice as it worked its 

 way along tore out of their places the blocks of rock which 

 at all levels had been disconnected by the hard frost of the 

 elevation just passed. These were deposited on the eroded 

 25 feet beach and on the shore line as previously described 

 (see Photo 14). On the North of the island they can 

 be seen in hundreds lying in confusion as they were left by 

 the ice. On the West coasts they lie in fewer numbers but 

 still are numerous. 



In observing these care must be taken to differentiate 

 between the stones of this period and others which have 

 fallen on to the beach in much more recent times. For 

 instance, near Lihou, a block carved out into a shallow basin 

 rests among the frost-riven blocks. This comes about in the 

 following way. The 25 feet beach has been eroded off the 

 foreshore, and with it the later deposits which had covered in 

 post-Grlacial times and in Neolithic times, and the blocks of 

 the Glacial time were lowered down as the undercutting 

 proceeded; but as all accumulations of later periods, including 

 the Neolithic soil and its contents, were above the blocks, the 

 removal of the soft earth, sand, etc., forming the shore let 

 down the whole contents of the accumulated deposits, and the 

 large stones which the present sea has not moved find them- 

 selves jumbled together. 



A good example of mixture of deposits bearing on this 

 period is to be seen at Rousse (see Diagram 5). The ice- 

 borne rocks which fell on the 25 feet beach rested on it 

 before it hardened into a conglomerate, and the action of ice 

 pressure assisted by tidal movement caused a partial redistri- 

 bution of the beach and partly buried the blocks. In course 

 of time the beach became hardened and the blocks cemented, 

 making it look as though the frost-riven blocks were laid 

 down first. This is disproved by the fact the beach is also 

 beneath them. The jumble is further increased by the recent 

 discovery of Neolithic cists also resting on the 25 feet beach. 

 The true place of these cists as regards their position will be 

 made clear when I discuss the Neolithic period towards the 

 close of the paper. I have introduced the subject here to show 

 that care must be taken in reading the evidence. 



The comparative freedom of the East coast from the 

 blocks forming the first part of the " Head " is, I think, 

 accounted for by the fact that the Small Russel was not open 

 in the same way as it is now. 



H 



