On Marine Deposits of Pumice . 339 
of 13,000 or 14,000 feet, whilst the islands of Fernando 
Po, St. Thomas, &c. are equally volcanic in origin.* 
Bearing in mind all the circumstances of the cases 
above quoted, it will, I think, appear that no good evi¬ 
dence has been adduced to justify the notion, that dust 
from the African desert has been, so far as these cases 
bear witness, met with at any considerable distances from 
the coast of Africa ; the dust on Etna in 1830 (being of a 
doubtful origin), is the best proof there can be found to 
confirm the contrary notion: whereas it appears that dust 
is carried to enormous distances from volcanoes in action.+ 
But little has been mentioned in this memoir of 
pumice ; but there are instances recorded of vast quan¬ 
tities having been met with at sea immediately after 
volcanic eruptions from craters near the coast or in is¬ 
lands. References to them can only be general, as they 
are easily made in the writings of those persons who 
describe violent terrestrial convulsions. 
1 here are, however, two cases of the kind which may 
not be improperly introduced here. The first is that of 
the shoal of pumice met with by Mr. Dove, on the 22nd 
March, 1724-5J, and by a number of other persons in 
different voyages through the same part of the sea. 
They are described as lying in drift from N.N.E'. and 
S.S.W., extending through a space of more than 317 
miles. Mr. Dove sailed through them for four full days, 
in lat. 35° 36' to 37° 54' S., and long. 0° 38' E. to 4° 9' 
W. They varied from the size of small pebbles to that 
* Owen's Voyages, vol. iL, p. 304. 
t It is perfectly irrelevant to the subject in hand to allude to the 
cases of stones and dust falling from the sky in ancient times, as 
mentioned by Roman and Greek historians; but it may be ob¬ 
served, that the evidence of modern examples justifies the belief, 
that the reports met with in Livy and other writers are not so 
fabulous as many persons imagine. 
I Phil. Trans., 1728. 
