114 
AMERICAN GEOLOGY. 
cone is built up about the orifice of the loosely coherent ma¬ 
terials. 
Volcanic action is not accompanied with the same pheno¬ 
mena at different times; neither do the different volcanoes eject 
the same kind of material at different epochs of eruption. At 
one time it is a thick heavy lava, which pours over one or two 
sides of the crater, and slowly flows down the mountain. The 
volcanoes of the Sandwich islands are boiling pools of melted 
rock—excavations rather than craters, and their activity is 
accompanied with moderately loud explosions, and the shrill 
hissing of steam issuing from a boiler. Sometimes, again, the 
volcanic products consist of ashes, which fall in part around the 
crater, while the finer particles are driven to distant countries 
by the winds. While the ordinary products of volcanic action 
consist of melted rock sufficiently liquid to flow, or of commi¬ 
nuted rock in the condition of an ash, there are still many other 
products which escape at certain times from different vol¬ 
canoes. Thus gases and vapors are common. Among them 
are nitrogen, ammonia, carbonic acid, carbureted hydrogen, 
and sulphureted hydrogen; boracic acid also escapes in the 
steam in company with ammonia. Hot water, holding silica 
in solution by means of potash or an alkali, is a common pro¬ 
duct of volcanic action in Iceland. Bitumen and naptha also 
are found among those products, especially at Taman, at the 
western extremity of the Caucasus, and at Baku, a port on the 
Caspian sea. The latter are mud volcanoes or salses, the bitu¬ 
men and naptha being derived from the superficial deposits of 
organic matter. The strongest indication of volcanic action in 
our own country was exhibited at New Madrid in 3811. The 
hot springs of Wachita, and those of California, witnessed by 
Mr. Forrest Shepard, must be regarded as due to a feeble vol¬ 
canic action. 
A phenomenon which stands connected directly or indirectly 
with volcanic forces, is the earthquake. It immediately pre¬ 
cedes, and perhaps continues during the first outbursts of this 
force. The earthquake consists essentially of movements of the 
