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ME. GEOEG-E H. DAEWIN ON THE INFLUENCE OF 
The essential point is, to compare the final and initial distributions of matter, after and 
before a period of large geographical change. 
17. Areas of subsidence and elevation. 
When a new continent is being raised above the sea, there is no certainty as to the 
extent to which areas in the adjoining seas partake in the elevation ; even in the case 
of S. America, where the area of elevation is supposed to be abruptedly limited towards 
the west, the line of 15,000 feet depth lies a long way from the coast. 
As soon, moreover, as the land is raised above the sea, the rivers begin washing away 
its surface, and the sea eating into its coasts. The materials of the land are carried 
away, and deposited in the surrounding seas. Thus to form a continent of 1000 feet in 
height, perhaps entails an elevation of the surface of from 3000 to 4000 feet, and all 
the matter of the additional 2000 to 3000 feet is deposited in the sea. This tends to 
make the adjoining seas shallower, and to cause some increase to the area of the land. 
Therefore in a sealess globe the effect must be represented by a greater area of elevation 
and a less height. 
The bed of a deep sea is hardly at all subject to erosion, and therefore the tendency 
seems to be to make the negative features of an ocean-bottom more pronounced than the 
positive features of mountain-ranges, at least in the parts very remote from land. 
The areas, then, of existing continents may not be a due measure of the areas of 
effective elevation ; we can only say that the latter may considerably exceed the former. 
The direct evidence as to the extent of the earth’s surface over which there has been a 
general movement during any one period, is also very meagre. It appears certain that 
very large portions of S. America have undergone a general upward movement within 
a recent geological period ; but there is no certainty whatever as to the limits of this 
area, nor as to whether the beds of the adjoining seas have partaken to any extent of 
this general movement. Thus the case of S. America is of scarcely any avail in deter- 
mining the point in question. The presence of deep ocean up to the Chilian coast 
seems, however, to make it probable that areas of elevation are more or less abruptly 
divided from those of rest or subsidence. 
There is only one area of large extent in which we possess fairly well-marked evidence 
of a general subsidence; and this is the area embracing the Coral islands of the Pacific 
Ocean. The evidence is derived from the structure of the Coral islands, and is confirmed 
in certain points by the geographical distribution of plants and animals. Some natu- 
ralists are of opinion that there is evidence of the existence of a previous continent ; 
others (and amongst them my father, Mr. Charles Darwin) that there existed there 
an archipelago of islands. In this dearth of precise information, only a rough estimate 
of area is possible. 
My father, who has especially attended to the subject of the subsidence of the Pacific 
islands, has marked for me, on the map given in his work on Coral Reefs, a large area 
which he believes to have undergone a general subsiding motion. This area runs in a 
