18J5.J NUMBER OF CRATERS. 376 



of volcanic rocks ; a few fragments of granite curiously glazed 

 and altered by the heat, can hardly be considered as an excep- 

 tion. Some of the craters, 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 hesitate to affirm, that there must be in the 

 whole archipelago at least two thousand craters. These 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 sides, or quite broken down 

 and removed. As all these craters 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 surround- 

 ing 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 very sterile, the 

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

 damp climate and a tolerably luxuriant vegetation. This is 

 especially the case on the windward sides of the islands, which 

 first receive and condense the moisture from the atmosphere. 



In the morning (17th) we landed on Chatham Island, which, 

 like the others, rises with a tame and rounded outline, broken 

 here and there by scattered hillocks, the remains of former 

 craters. Nothing could be less inviting than the first appear- 

 ance. A broken field of black basaltic lava, thrown into the 

 most rugged waves, and crossed by great fissures, is every where 

 covered by stunted, sun-burnt brushwood, which shows little signs 

 of life. The dry and parched surface, being heated by the noon- 

 tfay sun, gave to the air a close and sultry feeling, like that from 



