Co. XX.] 



ST. MICHAEL'S MOUNT, CORNWALL. 



539 



lie iolibouriiig cliffs were also undermined at many points on 



limestone 



Mount, Cornwall. — When 



great amount of change caused by the undermining power of 

 the waves, and by landslips in the last three or four cen- 

 turies on our eastern and southern coasts, and the proofs of 

 submergence of numerous forests which have sunk at some 



om 



becomes 



of surprise that we should find a single point where the out- 

 line of the present coast can be demonstrated to have re- 

 mained for nineteen centuries unaltered. Tor this reason St. 

 Michael's Mount in Cornwall deserves our special attention, 

 for it can be shown that all the characteristic features in its 

 physical geography have been retained throughout that long 

 series of centuries identically such as they now are. 



The Mount (see figs. 51, 52, and 53, pp. 540 and 541) con- 

 sists chiefly of granite, with some slate rock, like that of the 

 adjoining coast. It is 195 feet high, with precipitous sides, 

 and is situated near the head of Mount's Bay, which is dis- 

 tant about ten miles eastward from the Land's End. Twice 

 in every twenty-four hours this mount is an island, and twice 

 when the tide falls it is connected by a narrow isthmus with 

 the mainland. This isthmus is composed of the slate before 

 mentioned, the same which enters into the structure of part 

 of the Mount, where it is penetrated by veins of granite at 

 the junction of the two formations. At the highest spring 

 tides there is no less than twelve feet of water on the isth- 

 mus, and six at neap tides, in ordinary weather it is usually 

 dry for five hours at low tide. The annexed views will give 

 the reader an idea of the appearance of the 

 and low water.* 



Mount 



As there is no other rock on our coast which is twice 

 alternately an island and a promontory every twenty-four 

 hours, this circumstance alone would be almost conclu- 

 sive in favour of the opinion, that the Mount is the Ictis of 

 Diodorus Siculus. That historian, writing in the year 9 B.C., 



* For the original of figs. 51, and 52, I am indebted to the kindness of Sir 

 Henry James. 



