PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 127 
cially during the cainozoic period, is well known; but even if 
the surface of the oceans were to sink from one thousand to 
eighteen hundred fathoms, it would still be possible to recognize 
in the rough the present outline of our continents. Hence it 
would seem as if that outline were intimately connected with 
their earliest appearance and the subsequent evolution of the 
continent, and that these masses are not merely due to acciden- 
tal denudation. 
The view of the great age of our continents and oceanic 
basins was probably first suggested by Guyot; it was indepen- 
dently taken up by Dana, and Agassiz was perhaps the first to 
show that the results of the earlier deep-sea dredging expedi- 
tions added materially to the correctness of this view. Subse- 
quently Thomson, Geikie, and Carpenter elaborated this theory, 
which of late has gained ground among geologists, and has 
found its most recent advocate in Wallace. 
The geological structure of the different islands of the world 
enables us to judge whether they are mere volcanic peaks, the 
highest points of districts subject to cataclysmic local elevations, 
or whether they are parts of larger masses of land first built up 
by sedimentary deposits, and gradually reduced by denudation 
to their present size, — the remains, in fact, of great submarine 
banks, indicating in a certain measure the former outlines of 
the land. The extent of this denudation has been calculated 
in some cases; and so powerful is its agency, that, if carried on 
during long periods of time, it may transform oceanic regions 
into continental masses, and the reverse. This may have been 
the case in the earliest periods of the formation of the earth’s 
crust, when the precipitation was much greater than now; but 
we have as yet no evidence of any such transposition of conti- 
nental masses and of oceanic basins since the mesozoic period. 
If such pre-archiean continents existed, they, like the continents 
from which the materials for the mesozoic and tertiary deposits 
were derived, have left no traces. 
1 The careful examination of St. Paul’s having, as shown by Geikie, nothing what- 
rocks by the Abbé Renard, for instance, ever to do with the remains of a former 
clearly proves this island to be of volcanic continent, the long lost Atlantis. 
origin, like many other oceanic islands, 
