PERU. 237 
two days before us. We found the current generally with us, but not 
strong. The temperature of the water varied at sea from 58-27° to 66-5°, 
that of the air, from 57-3° to 63-04°, a rise of eight degrees in the former 
and six degrees in the latter in twenty-one degrees of latitude. 
On receiving the reports of the commanders of the different vessels, 
active operations were at once begun to refit, replenish our stores, and 
complete our duties. The necessary changes in officers and men 
were made, in consequence of my determination to send the Relief 
home. This I did on several accounts. I have stated that from the 
first I found her ill adapted to the service ; her sailing I saw would 
retard all my operations, and be a constant source of anxiety to me ; 
and I felt that I already had objects enough without her to occupy 
and engross my attention. The expense was another consideration, 
which I conceived myself unauthorized to subject the government to, 
particularly as I found on calculation, that for one-tenth of the sum it 
would cost to keep her, I could send our stores and provisions to any 
part of the Pacific. 
We found it necessary to have the Relief smoked, in order to 
destroy the rats with which she was infested, to save our stores 
from further damage. During this time the repairs of the Porpoise 
had been completed, and the usual observations for rating our 
chronometers, and with the magnetic instruments, were made on 
shore; and such officers as could be spared allowed to visit Lima. 
The naturalists were also busy in their several departments. We 
remained at San Lorenzo ten days, during which time its three 
highest points were measured with barometers at the same time. 
The result gave eight hundred and ninety-six feet for the southern, 
nine hundred and twenty for the middle, and twelve hundred and 
eighty-four feet for the northern summit. Upon the latter the 
clouds generally rest, and it is the only place on the island where 
vegetation is enabled to exist, The others are all barren sandy 
hills. It is said that the only plant which has been cultivated is 
the potato, and that only on the north peak. This becomes possible 
there from the moisture of the clouds, and their shielding it from 
the hot sun. 
The geological structure of the island is principally composed of 
limestone, clay, and slate. It presents a beautiful stratification. 
Gypsum is found in some places between the strata, and crystals of 
selenite are found in one or two localities. Quantities of shell-fish 
are found on the shore, and the waters abound with excellent fish. 
vol. i. 60 
