1916.] THE DEPOSITS. 375 



The height of these hills above the present high levels 

 must have been considerable, for the result of their future 

 disintegration covers the whole island with a mass of clay, 

 sands and gravels of all depths, of from 3 feet to 20 feet, and 

 represents an enormous weight of material. I am aware 

 that some believe that the clays which will form the subject of 

 a future chapter were brought to the island by floating ice, 

 but I have found no evidence of this, for all the boulders, 

 pebbles and angular pieces of rock found in the clays are of 

 local origin. So far I have not found any erratics. One 

 piece of striated schist seemed to me to be identical with a 

 specimen from the neighbourhood of Cherbourg ; but it was 

 examined by Professor Bonney who showed it to be of local 

 origin. (See r Fransactions, G. S. N. Sc, 1914.) 



Assuming, therefore, that the wastage of material which 

 occurred later on was all of local origin, we have to make 

 large increases in the heights of the hills on the upper plateau 

 of the island, for that plateau is now a flat plain relieved only 

 by the curves of the beginning of the valleys. 



We do not find these outcrops now, but we do find their 

 bases, and Avherever they are visible they show a smooth 

 surface with a lowering in the direction of the valleys. 

 These facts point to a weighty mass of ice moving over the 

 top of the island and slipping down the valleys. The move- 

 ments no doubt wore down the irregularities of the hard rocks, 

 filled in the inter-spaces and marked their impress on the 

 slopes of the valleys. 



At the same time that very weight and movement would 

 have a tendency to reduce the bosses and hills to a level, for 

 the ice-cap was not uniform either in thickness or stability as 

 it was of necessity weakened by summer losses on the slopes 

 and by the falling of the ice-overlaps on the cliffs, and was 

 moreover increased by each winter's snowfalls. 



That some such action was going on is also proved by the 

 fact that the clays that follow were laid down on an eroded 

 surface. 



The places worked as brick-fields all exhibit the features. 

 They are topped by clay which shows a distinct line where it 

 rests on decomposed rock. (See Diagrams of St. Martin's, 

 St. Andrew's, Fauconnaires and Vrangue, No. 6.) 



That the cause of this line of erosion was a moving- 

 weight is evident by the fact that the line follows the slopes 

 of the hills and stretches across any small pockets where the 

 softer material was protected. 



