366 Transactions.—Geology. 
Where two neighbouring craters are sometimes in eruption together, and 
sometimes not, the separating walls of the different channels are supposed 
to be melted down, or formed by solidification, as might be required to 
meet the case. 
These explanations are, however, nothing better than accounting for 
the earth’s stability by placing it on an elephant’s back. We are not told 
on what the elephant stands, nor what causes the subdividing channels. 
The explanation, indeed, requires explaining more than the subject matter. 
Even if any amount of central fluid be granted, and channels sub- 
dividing it, the walls of which are formed or melted to meet every case as: 
it may suit the convenience of the volcanologist, it is difficult to see how 
it explains volcanic action. The fluid matter either expanded, or it did not, 
after it received its excess of heat beyond that of the neighbouring solid 
masses. If it expanded, it would have no more tendency to rise to the top 
of a voleanic mountain, or even to rise a foot above its former level, than 
the Niagara River has to change its direction and run up the falls ; if it 
did not expand, its excess of heat would be transmitted to the rest of the 
earth’s mass at the rate of a mile a second, and it would not remain an 
hour in the fluid state, unless indeed it had sufficient heat to reduce the 
whole earth’s mass to a fluid state along with it. 
On our hypothesis, however, each volcano is separate and distinet—they 
are all due to an clevation extending over great distances, causing local 
action wherever the local circumstances are favourable. They may, there- 
fore, burst. out together or, not; may remain long in eruption, or only a 
second or two, without in the least invalidating the hypothesis. 
It is difficult to conceive how a channel of subterranean communication 
can exist over such great distances as are sometimes embraced in a volcanic 
throe. In 1755, for instance, when Lisbon was nearly destroyed by an 
earthquake, Kitlugja, in Iceland, burst into violent eruption, while the 
lakes of Scotland were at the same time thrown into oscillation. It would, 
however, militate greatly against our hypothesis if such long lines did not 
exist. 
There remains one other test to which we can subject this hypothesis, 
but I am sorry to say I have not been able to collect sufficient information 
to apply it. 
As stated above, the primary cause of all movement of elevation is the 
lengthening of the polar diameter of the earth. I have assumed that the 
elongation necessary to cause fracture is so small that the daily tides would 
greatly influence the time and manner in which it would take place, which 
it would do even if the crust were strong enough to resist a considerable 
elongation of the polar axis. 
cia alam 
Ae ea) Teer Seti). ay dene wee 
