REVIEWS 497 
since volcanic outbreaks are also accompanied by earthquakes often felt over 
large areas. 
4. Not all earthquakes lead to eruptions, but if the shocks in a given region 
cease on the eruption of a neighboring volcano, we may feel sure that the forces 
producing the eruption also produced the antecedent earthquake shocks felt by 
the surrounding country. 
5. That steam is the cause of volcanic eruptions is proved by the distribution 
of active volcanoes about the seashores and by the innumerable eruptions which 
occur in the depths of the ocean, whereas such vents always die out inland; and 
moreover by the fact that of the vapors emitted from volcanoes 999 parts in 
1,000 is estimated to be steam, the remaining one-thousandth part being by- 
products incidental to the moisture and high temperature. 
6. The vera causa of volcanic action and of certain earthquakes thus estab- 
lished for some particular cases must be held to be the universal cause in all 
cases whatsoever, according to Newton’s rule of philosophy. 
7. The heaving of steam accumulating within or just beneath the earth’s 
crust is therefore the true cause of all world-shaking earthquakes, and volcanic 
outbreaks occur only when an outlet is forced through to the surface, which usually 
happens in mountains, where the earth’s crust is already badly fractured and 
upheaved. 
8. When the subterranean steam pressure becomes great enough to shake 
the earth’s crust, it naturally moves at the nearest fault line, where the rocks are 
broken, but the movement observed is the result, not the cause of the earthquake. 
g. Volcanoes are particular mountains blown open by steam pressure under 
the throes of earthquakes (cracks in the rocks appear to be the beginning of 
some few volcanoes), and since all volcanoes blow out pumice and ashes, these 
materials must be held to exist in all mountains, and are made by the inflation 
of molten rock with steam and other vapors. 
to. Any mountain peak, therefore, is capable of becoming a volcano if the 
subterranean steam pressure be sufficiently powerful to break open an orifice. 
But orifices close up and volcanoes die out inland and elsewhere if the supply 
of steam is inadequate to keep open the vents upon which the activity depends. 
Even if stopped up for a time, later heaving of the earth may give the volcano 
renewed activity, and when the mountain has been dormant for a long time it 
is found that the violence of the eruption is greatly increased. The violence of 
the subterranean pressure in such a case approaches that of a region which 
has no vent at all, and hence we see why earthquakes in non-volcanic regions 
frequently become so terrible, because the forces accumulate to frightful fury 
before any relief whatever is afforded, and the result is a most terrible earthquake. 
11. The mountains are formed by the injection of steam-saturated lava 
under the coast, which breaks the overlying surface rocks and gives rise to a 
ridge parallel to the sea. This is why all mountains are formed parallel to the 
seashores. 
