NUMBER OF CRATERS. *7 



fragments of granite curiously glazed and altered by the heat, can 

 hardly be considered as an exception. Some of the craters, surmount- 

 ing the larger islands, are of immense size, and they rise to a height ot 

 between three and four thousand feet. Their flanks are studded by 

 innumerable smaller orifices. I scarcely hesitate to arhrm, that ther 

 must be in the whole archipelago at least two thousand craters. Ihese 

 consist either of lava and scoriae, or of finely-stratified, sandstone-like 

 tuff' Most of the latter are beautifully symmetrical ; they owe their 

 origin to eruptions of volcanic mud without any lava : it is a remarkable 

 circumstance that every one of the twenty-eight tuff-craters which were 

 examined, had their southern sides either much lower than the other 

 Culpepper I. 



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apparently have been formed when standing in the sea, and as the 

 waves from the trade wind and the swell from the open Pacific here 

 unite their forces on the southern coasts of all the islands, this singular 

 uniformity in the broken state of the craters, composed of the soft and 

 yielding tuff, is easily explained. 



Considering that these islands are placed directly under the Equator, 

 the climate is far from being excessively hot ; this seems chiefly caused 

 by the singularly low temperature of the surrounding water, brought 

 here by the great southern Polar current. Excepting during one short 

 season, very little rain falls, and even then it is irregular ; but the clouds 

 generally hang low. Hence, whilst the lower parts of the islands are 



