W. O. Crosby— Origin of Continents. 201 
Australia, while the sea in its near neighbourhood has a depth of 
from 15,000 to over 17,000 feet ; and yet it is composed of stratified 
Eozoic, Paleozoic, and Mesozoic rocks. The Salomon Islands, 500 
miles from New Guinea, and nearly twice that distance from 
Australia, are, according to Garnier, composed of rocks similar to 
those found in New Caledonia. Kerguelen Island, in the southern 
part of the Indian Ocean, and 2,000 miles from the nearest continent, 
is certainly a true oceanic island; and yet it is composed, in large 
part, of stratified rocks, both fossiliferous and crystalline. The 
Philippine Islands contain Secondary, if not Paleeozoic, strata; and, 
although only separated by from 300 to 500 miles from Borneo and 
the continent of Asia, they are surrounded on all sides by water from 
two to three miles deep. Naturalists are generally agreed that the 
true borders of the continents are not the actual shore-lines, but the 
lines, sometimes one to two hundred miles from shore, where the 
water commences to deepen rapidly and the abysses of the ocean 
begin. All land beyond this true continental edge is oceanic. Now, 
judged by this criterion, the Philippines are, apparently, oceanic 
islands. It is certainly unreasonable to say that all oceanic islands 
must be remote from the continents. As well might it be claimed 
that all the higher parts of the continents, or mountains, must be 
remote from the sea. I have been informed by Prof. Jules Marcou 
that the Marquesas Islands, lying on the eastern border of Polynesia 
and near the centre of the Pacific, contain representatives of the 
older stratified formations. Paleozoic and Mesozoic rocks are well 
developed in Spitzbergen, which, it would seem, may be fairly 
classed as an oceanic island. Again, many oceanic islands have not 
been examined geologically with sufficient care to justify Mr. 
Wallace’s sweeping and positive statement that, with two exceptions, 
none of them contain any traces of the older stratified formations. 
With the exceptions noted, the oceanic islands are nearly all 
small, and are composed of eruptive rocks or of coral-reefs resting, 
presumably, upon a volcanic foundation. The oceanic islands are, of 
course, merely the tops of submerged mountains; and it is only 
with the highest points of the continents that they can be properly 
compared. Now, supposing the existing continents were submerged 
to an average depth of 15,000 feet, what would be the geological 
character of the land remaining above the sea? Paleozoic and 
Mesozoic rocks would probably be about as scarce in it as in modern 
oceanic islands. Asa rule, the loftiest mountains of the globe are 
composed of eruptive rocks, and in many cases they are extinct, 
or even active, volcanoes; although the main mass of every mount.in 
system is formed of stratified formations. The volcanic materials 
usually constitute but a small part of the whole; but they are the 
cap-sheaf. 
Granting, however, for the sake of the argument, that the older 
fossiliferous formations would be left above the water in some cases ; 
if the islands of this class were large, they are fairly represented in 
the modern ocean by New Zealand, New Caledonia, and Spitzbergen, 
and, if small, by the Seychelles, Salomon and Marquesas Islands and 
