196 EARTHQUAKES. 
sure originating ina general subterranean liquid mass. 
Thus, for example, in the crater of Mauna Loa the lava 
stands ‘‘ ten thousand feet higher than in the crater of 
Kilauea, only twenty miles distant.” 
We may admit that voleanoes act as safety-valves for 
the pent-up telluric forces, and, by their sudden explo- 
sions, become true causes of certain earthquakes, with- 
out accepting, to its full extent, the common belief that 
there isa synchronism between volcanic eruptions and 
earthquakes. | 
Some of the great earthquakes of record have not only 
occurred at times when no volcanic phenomena have 
taken place, but they have occurred in places where vol- 
canoes did not exist, as at Calabria, Lisbon, and 
Charleston. 
On the other hand, that seismic and volcanic phenom- 
ena are often seen together is well established by the 
evidence given by Herculaneum and Pompeli. When 
Concepcion felt the great shock in 1835, there occurred 
two great submarine eruptions. When Riobamba was 
destroyed in 1797, Mount Pasto, one hundred twenty 
miles distant, suddenly ceased its activity, while volea- 
noes within the immediate vicinity of Riobamba were in 
no way affected. In 1861, a volcano at the base of 
which Mendoza is situated burst into eruption, when 
this city, with ten thousand of its people, was destroyed 
by an earthquake. 
Although many earthquakes have their origin in mid- 
ocean, it is, nevertheless, true, generally speaking, that 
they are more frequent in volcanic and mountainous re- 
gions, along ovean boundaries. And, while earthquakes 
and volcanoes may be but different effects of a common 
cause, the evidence at hand does not enable us to affirm 
that their phenomena have at all times any direct con- 
nection. 
Following Prof. Milne it may be stated that, as the re- 
80 
