Penny Blood: Serial Sensation and Working-Class Entertainment — page 241: what you’re looking at

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224 GEOLOGICAL MOVEMENTS [CH. XVII. less than the average thickness of the icebergs seen from the Challenger in the Antarctic ocean’. Similar movements have occurred, and are now going on in Greenland. Raised beaches are found up to 326 feet above the sea. But the land is now slowly subsiding at the rate of about from 6 to 8 feet per century. This may possibly be accounted for by the snowfall being at present greater than is carried off by the glaciers and by evaporation’*. It is clear that vertical movements of the earth’s crust will, according to our theory, be of two kinds; one resulting from the laws of hydrostatic equilibrium simply, and the other connected with compression. The former, although it may for a long time continue to lift up the rocks of a given area from below, can yet never by itself restore them to their pristine height. Degradation must always make more rapid progress than elevation. But the two are necessarily correlatives of each other. The degradation of the tract causes more rock to rise. up, to be in its turn degraded. Such slow and continuous upward movement explains how rivers can cut across the dip of hills, It explains the drainage of such areas as the Weald, and of valleys of elevation on even a grander scale. It explains perhaps even the drainage of the great plateau of the Colorado region. It also explains the fact that we find what once were perhaps river gravels perched on the highest hills of a district. But the vertical movements arising from compression are of a different character. The effect is to elevate a tract to a higher average level than before. There may be troughs and depres- sions formed by it, but their amount will be more than counter- balanced by the elevations. The internal heat of the earth is the ultimate cause of this class of movements. The contrac- tion of the interior from cooling may possibly contribute to 1 Sir Wyville Thomson, ‘‘On the Conditions of the Antarctic,”’ Nature, Vol. xv. p. 105, states that these stand about 200 feet high above water. Calculating from a specific gravity of 0°92 this gives 2,500 feet for the entire thickness. 2M. Johnstrup, ‘On the Interior of Greenland,’ reviewed in Nature, Vol. xxi. p. 844, 1880. The above passages were written before the appearance of Mr J. S. Gardner’s article in the ‘‘Geol. Mag.” Dec, 2, Vol. vim. p. 241, where somewhat similar views are propounded. COLA @ NOOKS ACO | on