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ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA. 65 
the volcanoes known to exist upon the earth’s surface are found, dotted 
along these ridges or crests in an unequal and uncertain manner. 
And as our oceans and greater seas are bounded, and below their water- 
surface subdivided, by these ridges, along the lines of which the volcanic 
foci are found; so, as long observed, it is a fact that all active volcanoes are 
comparatively close to the sea, or to some large body of water; indeed, 
they could not present the phenomena they are known to do, without a 
supply of water, and nearly always of sea-water, more or less constant and 
plentiful, derived from this propinquity. (See Trans. R. I. Acad. vol. xxi. 
pp- 98, 99.) 
However different, then, may have been the train of forces upon which the 
elevation of the mountain-chains and other relatively raised lines of the pre- 
sent surface have depended, from those which now produce the ejections 
thrown up by volcanic action, the latter seem to follow upon the traces of 
the former ; and we shall find that the earthquake generally does so likewise. 
The distinction long made, into linear and circularly grouped or clustering 
voleanoes, I conceive has no foundation in nature, By far the largest pro- 
portion of all the volcanic vents over the whole earth are found arranged 
along the flowing lines of mountain-chains. 
The so-called clusters or cireulur groups never are found covering surface- 
areas larger, if so large, or more widely apart, in any single group, than those 
within which volcanic vents are found that undoubtedly belong to linear ar- 
rangements (Mexico for example). 
Nearly all the clusters or circular groups of volcanoes are situated in the 
ocean, and far from continental land ; they stand on, and are connected with 
each other, by oceanic plateaux, rounded submarine ridges, shallows, rocks, 
and islands, and by similar connexions with points of continental coasts, 
either mountainous or volcanic. The conclusion seems justifiable, that 
‘these clusters or groups are the gnly visible points, “few and far-between,” 
situated along sub-oceanic linear volcanic ranges, along which the open 
vents are probably much fewer than along equal lengths on land, but still 
marking as truly as the most thick-set linear vents the great lines of fracture 
of the earth’s crust. Were this the proper place, much might be adduced 
in support of this view of volcanic distribution. 
The connexion between volcanic and seismic effort is so obvious, although 
the nature of their connexion has been so little understood, that we are 
prepared to find the deepest tints of the seismic map fringing off from those 
great mountain-ranges where the volcanic foci stand close in rank; but it 
was not before so apparent that, along the elevated ridges or mountain- 
ranges that gird and divide the great surface-basins, even when not volcanic, 
or when volcanic foci are rare and widely separated, the earthquake is still 
found to range in broad bands, following the general line of the crest. 
Upon a very much minuter scale of survey than we are now occupied with, 
such would seem dependent upon the physical fact, that the earth-wave 
will be best and furthest propagated through the most solid and elastic line 
of material, that is, in the axial line of mountain-chains and valleys, as is 
found to be the case; but the indication of our map is a far more extensive 
one, and points to some different and deeper cause. Thus, to resume our 
Seismic survey of the Map, Iceland, Ferro, Shetland, and the south-west 
coast of Norway, nearly to Christiania, form a broad band of seismic con- 
nexion, which would probably run on to Greenland, and along its coast to 
Jan Mayen, did we know anything of their earthquake history. 
_ The fact (if it be so), that the west coast of Greenland, in Davis's Straits, 
is sinking gradually, would in nowise conflict with the probability of 
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