THE GEOLOGICAL PUZZLE PRESENTED BY 

 THE MOULIN HUET AND ICART CAVES. 



READ APRIL 26th, 191 1 



The caves at Icart and Moulin Huet have, ever since the 

 first visit of the Society in 1883, offered a puzzle which up to 

 now no one has attempted to unravel, but the work of the 

 Geological Section in the recording of the deposits of the 

 island has made it possible to give an explanation, for light 

 has been thrown on the succession of the deposits found in the 

 caves. (See " Pleistocene Period in Guernsey " in this year's 

 Transactions.) 



The late Mr. G. T. Derrick, then the leader of our 

 geological section, thus describes the Icart caves. " There is 

 no doubt that the Avhole cave was filled with pebbles 

 (apparently from the beach below) for they are found adhering 

 to the walls and roof, cemented to them by secretions of 

 carbonate of lime." 



To account for pebbles having filled a cave some 30 to 40 

 feet as regards its roof, above the mean sea level, and yet have 

 come from the present beach, Mr. Derrick offered the follow- 

 ing explanation : — 



"My idea is that, ages ago, the cave opened out to the 

 beach " (the opening had been described as having been closed 

 with a concrete of pebbles) " which may have been from 

 10 to 20 feet higher than at present; at this point the cave 

 was filled with sand and pebbles." 



A study of the levels has proved that such an explanation 

 is impossible, for the conglomerate as regards the lower ledge 

 is now identified as being the top of the 25' beach. This 

 identication might seem to make the question more obscure, 

 but it will presently be seen that there really is no puzzle at 

 all when all the facts are known. 



By a detailed description of the cave at Moulin Huet I 

 shall be able to bring all the facts clearly before you. 



The cave is not a cave in the same sense as many of the 

 others on our south coast. At one time it was a mere cleft 

 and quite open above and below. Now it is open below but 

 closed above. The cave is entered from the present beach 



