1835.) | NUMBER OF CRATERS. 873 
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 scoriz, 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 Java: 
it isa 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. Asall 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- 
day sun, gave to the air a close and sultry feeling, like that from - 
