220 RAISED BEACHES, CLIFF AND RUBBLE HEADS. 



ICART POINT 



There exists a deposit of shingle in an old cave; this has been 

 described by Mr. Derrick * who believes that the whole cave 

 was filled with pebbles and afterwards cemented into a con- 

 glomerate. The same conditions exist at the cave at 



MOULIN HUET. 



Here we have a cave opening from the beach by a narrow 

 passage which has been produced by the wearing away of a 

 comparatively soft vein in the gneiss. Once inside we find a 

 ledge of rock extending the length of the cave at its back, and 

 standing about three and a half feet above the present shingle 

 floor of the cave. This height varies, for the shingle of the 

 floor is moved about by extreme high tides so as to alter its 

 level from time to time. On the ledge is a similar mass of 

 conglomerate as found in the Icart cave. We may speak of 

 it as being about four feet in thickness on the ledge, but in 

 reality this is but a remnant, for the back, upperside and roof 

 of the cave is plastered over with the cemented beach stones, 

 proving that this cave also has been at one time filled with 

 pebbles. Before passing on to the consideration of other 

 deposits there are a few points to be noticed. First : the pre- 

 sent floor is undoubtedly lower by more than three feet than 

 when the deposited pebbles commenced to be attacked. Mr. 

 Carey and I have thoroughly and exhaustively examined the 

 cave, and are led to this conclusion by the following evidence. 

 On the level of the lower portion of the ledge of the cave, the 

 sides of the entrance are worn away by the attrition of the 

 loosened pebbles, but the lines thus produced are not directed 

 downward to the present sea-level, but are horizontal. It 

 follows, therefore, that the lower three feet of the present 

 passage was closed, either when the lowest layer of pebbles 

 was being laid or when the sea commenced, after centuries of 

 rest, to eat away the deposit. Second : The question of the 

 relative order of deposition and erosion is somewhat compli- 

 cated by the levels found. As stated in the heading of this 

 paper, the levels have been taken by Mr. Carey, and I know, 

 for I have worked with Mr. Carey through many of the 

 le veilings that nothing has been taken for granted. The 

 starting place for all the levels but one have been points, 

 the elevations of which have been previously ascertained by 

 Mr. Duquemin, who in his turn has used a mean sea-level, as 

 deduced by Mr. Lister and the engineers of the harbour, as the 

 zero. 



* See full description, page 81, Natural Science Transactions for 1889. 



