Ca XXIX.] 



ISLAND OF ST. PAUL— TEXERIEFE. 



643 



of such volcanic islands. It may be useful to cite, in illustration of 

 the same subject, the present geographical condition of St. Paul's or 

 Amsterdam Island, in the Indian Ocean, midway between the Cape 

 of Good Hope and Australia. 



In this case the crater is only a mile in diameter, and 180 feet 

 deep, and the surrounding cliffs were loftiest about 800 feet high, so 

 that iu regard to size such a cone and crater are insignificant when 

 compared to the cone and Caldera of Palm a or to such volcanic 

 domes as Mounts Loa and Kea in the Sandwich Islands. But the 

 Island of St. Paul exemplifies a class of insular volcanoes into which 

 the ocean now enters by a single passage. Every crater must almost 



Fi.ar. 702. 



View of the Crater of the Island of St. Paul. 

 Ei& 703. 



Side view of the Island of St. Paul (X. E. side). Nine-pin Eocks two miles distant. 

 (Captain Blackwood.) 



invariably have one side much lower than all the others, namely, that 

 side towards which the prevailing winds never blow, and to which, 

 therefore, showers of dust and scoriae are rarely carried during erup- 

 tions. There will also be one point on this windward or lowest side 

 more depressed than all the rest, by which, in the event of a partial 

 submergence, the sea may enter as often as the tide rises, or as often 

 as the wind blows from that quarter. For the same reason that the 

 sea continues to keep open a single entrance into the lagoon of an 

 atoll or annular coral reef, it will not allow this passage into the cra- 

 ter to be stopped up, but will scour it but at low tide, or as often as 

 the wind changes. The channel, therefore, will always be deepened 

 in proportion as the island rises above the level of the sea, at the rate 

 perhaps of a few feet or yards in a century. 



