Ty O}PiOIGRFAVE EE CeAyy EV RVA TD Ui RES. 429 
from volcanic action, for throughout the whole interior of America 
we find no evidence of such fires, and the remark applies almost as 
strictly to the whole eastern continent; they were extinct even before 
the early silurian epoch. Igneous eruptions over these extended re- 
gions have since been confined to fissure ejections. But over the Pa- 
cific Ocean, volcanoes have abounded: every high island in Polynesia, 
excepting New Zealand, is of igneous origin; and even the coral 
islands probably rest on a base of similar character. In the Atlantic 
too, the islands are of the same volcanic nature. We hence naturally 
conclude that the continental portions of our globe first cooled, and 
became solid, and that the intermediate parts cooling at a later period 
or less rapidly, contracted most, inasmuch as the crust was here 
thinner :—just as a lead or iron ball is often found to have the surface 
depressed on the side that cooled last. ‘The oceans were in general 
the more igneous portions of the globe, and the continents the parts 
which were first free from fires. 
This view is confirmed by the fact that the continent of America 
is nearly cut in two by the ocean where volcanic fires prevail across 
its track from east to west, and where, consequently, subsidence from 
contraction was longest continued ;—that the ast Indies, properly a 
southeastern prolongation of Asia, is another archipelago abounding 
in volcanoes, instead of being a part of the continent: that New Hol- 
land* and Borneo, and all large bodies of land, are free from volca- 
noes over their interior, and that all volcanic regions are in or near 
the ocean.t 
Our own investigations in the Pacific, following out the general 
deductions of Mr. Darwin relating to coral islands, have shown that 
this ocean has undergone a subsidence of several thousands of feet 
during the growth of coral. This would seem to be the close of the 
long period of subsidence which had been in progress from the 
remotest era. During the same period the continents have on the 
whole become more elevated than they were before, as tertiary beds 
* The only volcanic tract is one in South Australia. So in Borneo there are no yol- 
canic mountains known excepting those near the coast. 
+ This last fact has been attributed to the supposed importance of the ocean’s waters 
in promoting volcanic action, But if this would account for the absence of volcanoes 
from the interior of continents at the present time, what was the reason in the silurian 
period, for the absence of volcanoes from these same regions, then beneath the sea, or 
bordering it? It is obvious that some other cause must be assigned for the proximity of 
volcanoes to the ocean, 
108 
