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however, well out of any of the direct lines of volcanic energy, 
though we are, in common with the rest of the world, always liable 
to the minor earthquakes caused by the falling in of subterranean 
cavities, and the fractures and crushings of rocks which must 
necessarily be caused by the shrinking of the earth’s crust. As 
you all know, the earth, which was at one time a molten and glow- 
ing mass, has been for countless ages gradually cooling, and is, of 
course, doing so still. Itiscaleulated by Sir William Thompson 
that our globe loses each year sufficient heat, or caloric, to melt 
777 cubic miles of ice, or to raise an equal bulk of water from 69 
deg. Fahrenheit, to boiling point, 212 deg. This cooling is neces- 
sarily attended with contraction, and it is this shrinking of the 
earth’s surface which has thrust up the various mountain ranges, 
‘just asa withering apple in contracting thrusts upitsskin. The same 
process of contraction must be eternally going on beneath the 
_ earth’s surface, and must assuredly produce prodigious effects in 
the shape of heat and motion, accompanied necessarily by earth 
__ tremors and vibrations ; in fact by minor earthquakes. As regards 
volcanic eruptions, however, we have already had our day, in 
' long bygone geological (miocene) times, as evidenced by the vol- 
canic deposits in Wales, the North of Ireland, and several parts of 
_ England and Scotland. Snowdon and Cader Idris are both of 
volcanic origin, as is also the celebrated Giant’s Causeway. The 
way in which voleanic action shifts to different points of the earth’s 
: surface is most curious and unaccountable. There is scarcely a 
spot which has not been visited, while those centres where it is 
now most active were, in bygone ages, quite tranquil. The whole 
submarine strata, for example, on which Etna now stands, were in- 
times not geologically very remote, not existent. Nor is any 
instance known in which volcanic energy, after becoming extinct, 
has again returned to the same spot. So that, humanly speaking, 
we may be said to be tolerably safe, being, as I before remarked, 
out of the direct line of still active volcanoes. A glance at the 
map I have sketched will show you the curious linear arrange- 
ments of volcanoes, which run in a more or less north and south 
direction. As I have already pointed out, one would expect them 
_ to occur on the lines of greatest weakness of the earth’s crust, 
namely, where the ocean bed is depressed and the adjoining land 
_ elevated. And you will observe voleano outlets all more or less 
directly follow the outlines of the two great continents of America 
and Asia. If we imagine long cracks or fissures running, generally, 
.- in a north and south direction, and connected here and there by 
cross lines (just as might happen in a ball of drying clay), we 
_ Shall readily understand this linear arrangement of volcanoes, 
_ More especially if we accept the theory of water finding its 
