VI. 
THE PERMANENCE OF CONTINENTS AND OF OCEANIC BASINS. 
Tur outlines of our continents as they are defined on geo- 
graphical maps give us but an imperfect idea of their true 
shape. An examination of the relief of the globe as developed 
by soundings leads to very different conclusions concerning the 
connection of continents and of islands from those obtained by 
geographical data. The soundings have developed the great 
terrestrial folds, of which the continents are merely such por- 
tions as are elevated above the level of the sea. The latter 
have been modified by the action of atmospheric agencies ; their 
height has been reduced; and the material thus worked over 
from the earliest times has built up the sedimentary formations 
which have little by little been deposited on the flanks of these 
ancient continental masses, extending their outlines so as to 
cover larger and larger portions of the original folds in succes- 
sive geological periods. 
As the early soundings showed the existence of a former con- 
nection between Great Britain and the Continent, so more recent 
explorations have enabled us to understand the true relation of 
Tasmania and New Zealand to the Australian continent, with 
its adjacent archipelago, as it probably existed in the early part 
of the mesozoic period. Similarly, the soundings give us some 
idea of the relations of the East Indian Archipelago to the 
Asiatic continent. We have a very different conception of the 
relations of the insular groups of the Pacific to each other and 
to the tertiary Pacific continent, so often called upon to explain 
difficulties in the geographical distribution of the fauna and 
flora of these islands. We may now speculate with some de- 
gree of certainty on the former connections of Madagascar and 
1 Such folds are probably the Challenger and Dolphin ridges of the Atlantie. 
