VI. 



THE PERMANENCE OF CONTINENTS AND OF OCEANIC BASINS. 



The 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, extendino- 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 



^ Such folds are probably the Challenger and Dolphin ridges of the Atlantic. 



