_ Parr lL] THE OUTER SURFACE OF THE GLOBE, 35 
temperatures, the amount in the Atlantic surface water, between 
20° and 25° C., being 0:0466 gramme per litre, and in the surface 
Pacific water 0:0268. He points out the curious fact that, according 
to his analyses, sea-water contains sometimes at least thirty times as 

| -much carbonic acid as an equal bulk of fresh water would do, and he 

traces the greater power of absorption to the presence of the sulphates, 
II.—The Solid Globe. 
Within the atmospheric and oceanic envelopes lies the inner solid 
globe. ‘The only portion of it which rising above the sea is visible 
to us, and forms what we term Land, oceupiesabout one-fourth of the 
_ total superficies of the globe, or about 52,000,000 square miles. 
§ 1. The Outer Surface.—The land placed chiefly in the northern 
hemisphere is disposed in large masses, or continents, which taper 
southwards to about half the distance between the equator and the 
south pole. No adequate cause has yet been assigned for the present 
distribution of the land. It can be shown, however, that portions of 
the continents are of extreme geological antiquity. There is reason 
to believe, indeed, that the present terrestrial areas have on the whole 
been land, or have at least never been submerged beneath deep water 
from the time of the earliest stratified formations; and that, on the 
other hand, the ocean basins have always been vast areas of depression. 
This subject will be discussed in subsequent parts of this volume. 
In the new world the continental trend is approximately north 
and south ; in the old world, though less distinctly marked it ranges 
on the whole east and west. An intimate relation may be observed 
_ between this general trend and the direction of the mountain chains, © 
This is best exhibited by the American continent. In the old world, 
Kurope and Africa, though now disjoined, were once united, and may 
be considered as one continental. mass. Europe and Asia, on the 
other hand, though now united were partially separated in compara- 
_ tively recent geological times by a long inlet which extended for 
_ several hundred miles southward from the Arctic Ocean, and by the 
great Mediterranean Sea, of which the existing Black, Caspian, and 
Aral Seas are the shrunk remnants. Asia is linked with Australia 
by a great chain of islands; but there is no reason to suppose that 
the relation was ever closer than it is now. On the contrary, the 
great contrast between the Asiatic and Australian faunas affords 
good grounds for the belief, that at least for an enormous period of time 
Asia and Australia have been divided by an important barrier of sea. 
| While any good map of the globe enables us to see at a glance 
the relative position and area of the continents and oceans, most 
maps fail to furnish any data by which the general height or volume 
of a continent may be estimated. Asa rule, the mountain chains are 
- exaggerated in breadth, and incorrectly indicated, while no attempt 
is made to distinguish between high plateaux and low plains. In 
' Proc. Roy. Soc. xxiv. 9 
D 
