NUMBER OF CRATERS. 139 



and between five and six hundred miles westward 

 of the coast of America. They are all formed of 

 volcanic rocks ; a few fi-agments of granite, curi- 

 ously glazed and altered by the heat, can hardly 

 be considered as an exception. Some of the cra- 

 ters surmounting the larger islands are of immense 

 size, and they rise to a height of between three 

 and four thousand feet. Their flanks are studded 

 by innumerable smaller orifices. I scarcely hesi- 

 tate to aftirm that there must be in the whole ar- 

 chipelago at least two thousand craters. These 

 consist either of lava and scorige, or of finely-strati- 

 fied, 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 sides, or quite broken down and removed. 

 As all these craters apparently have been formed 

 when standing in the sea, ajid 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 yield- 

 ing tuff, is easily explained. 



Considering that these islands are placed direct- 

 ly under the equator, the climate is far from being 

 excessively hot. This seems chiefly caused by the 

 singularly low temperature of the suiTounding wa- 

 ter, brought here by the great southern Polar cur- 

 rent. Excepting during one short season very lit- 

 tle rain falls, and even then it is irregular ; but the 

 clouds generally hang low. Hence, whilst the low- 

 er parts of the islands are very sterile, the upper 

 parts, at a height of a thousand feet and upwards, 

 possess a damp climate and a tolerably luxuriant 



