214 On Earthquakes—their causes and effects. 
with amazing rapidity. through a channel similar to those 
described. 
many remarkable eruptions ‘of volcanoes are well 
calculated to prove the agency of the ocean. The mud- 
volcanoes of Macalouba in Sicily, tana. and Bologna in 
Italy, and those of the Crimea, of Java, and Iceland, must 
be caused by water, drawn from this source and ejected 
with the soil, intimately mixing with it on their passage to 
the summit of the crater. 
ions have taken place of dust only. A most re- 
mallet e of this kind happened very recently, 1815, at 
‘Tamboro, near Java, when such showers were thrown up as 
o produce total darkness a great distance. It continued to 
fall three hundred and thirty miles distant, for nearly a whole — 
y. This must: have been the sudden extrication of a 
slumbering mass which may have been accumulating for 
é ees in the bosom of the mountain 
The air-volcano of Cumacatar deseribed by Humboldt 
presents an anomaly, and is not easily accounted for, except 
on the tagiare that it may be an old yolcano, so near 
extinct as to have weak enough only to cause a continued 
draft or current 
irregu' rity “of eruptions of volcanoes and occur- 
r cinges of earthquakes, we have many curious instances. An 
ejection of ashes for a few minutes, is sometimes succeeded 
by a calm of ten years. In 1766 the city of Cumana was 
_ entirely destroyed in a few minutes, and shocks were hourly 
felt during a period of fourteen months. In 1692, Port- 
oyal, Jamaica, was destroyed, and the inhabitants were 
olnaed to remain on board of vessels for two months, on 
account of the continued concussions experienced there, In 
this earthquake persons were swallowed up, and by another 
effort of nature exhumed. Dr. J. W. Webster, in his descrip- 
tion of St. Michael, informs us that thirty-one shocks were 
felt in the city of Ponta Delgada, in the space of a few hours. 
In some parts of the chain of the Andes, eruptions take 
place regularly every thirty or forty years. 
t has been the anxious inguEy, of many geologists, in 
achat formation do volcanoes exist? is it necessary the 
Id be nourished by any particular stratum? Ip answer 
to these queries, it may be said that those persons who judge 
from the exterior of a bur rning mountain, which may be por- 
phyry or any transition orsecondary rock, that it necessarily 
