350 STABILITY OF OCEAN LEVEL. 



Moreover, to put an extreme case, it may be a condition that the land 

 shall sink so that water shall cover the whole surface. In this case 

 the level of the ocean would rise, that is, the mean radius of its 

 curved surface would be lengthened, by a quantity depending on the 

 mass of the solid land submerged, and on the relative area of land and 

 water. This relation of area is more than 3 water to i land. The 

 cubic content of the solid land may be thus estimated. In England, 

 Wales, and Scotland, the average height of those conspicuous moun- 

 tain masses which appear to give shape to the whole country is about 

 30,000 feet; and if we consider this as the apex of a cone whose base 

 is the whole area, we shall have the mean height of the land above 



3000 

 the sea = feet. The mountain masses, however, do not really 



affect, by their special elevation, more than a fraction of the area of 

 the British Isles ; the far greater part of the land depends on heights 

 not exceeding 1000 feet. If the mountain tracts be called half of the 

 area, and the hilly and more depressed parts half, we shall find the 



mean height of the whole mass of land I - ) = 666 feet. 



But on account of the valleys which divide the principal masses, we 

 may reduce this to say 500 feet. 



This principle applied to the continents of Asia and America would 

 give in round numbers about 2000 feet mean altitude of land; and as 

 the area of the expanded ocean would be four times as great as the 

 land is now, the total mean elevation of the water, by the submersion 

 of the whole mass of land, would be about 500 feet ; a quantity too 

 small to be of use in explaining any but the lesser order of geological 

 phenomena, and which may be considered as the extreme limit of 

 oceanic rise under these conditions. 



Secondly, We may suppose the existence of cavities into which 

 the solid land might sink, so that there may be no elevation in another 

 place corresponding to the given depression. To put this also to 

 extreme, we may imagine the very improbable case that a mass of 

 solid materials, equal in bulk to all the solid land above the water, 

 should sink into a cavity, and that the surface of the submerged land 

 should be level. The level of the ocean would be nearly unaltered, 

 except in a small degree, by reason of its shallow expansion over the 

 area of the land. We might go on to suppose even the enormously 

 improbable case of cavities existing so large as to admit twice the 

 whole solid mass of the continents, and that these should sink with 

 an equal bulk of materials into these cavities. Even in this case the 

 ocean level would only be lowered 500 feet. 



TJiirdly, If we suppose contemporaneous or successive elevations 

 and depressions, however extensive, the ocean level would oscillate 

 about a constant line. 



It is evident, therefore, that by no stretch of conjecture, that is 

 not absolutely absurd, can we torture the known laws of terrestrial 

 arrangements into agreement with the hypothesis of any but small 

 changes of level of the ocean ; a conclusion which enables us to 



