Penny Blood: Serial Sensation and Working-Class Entertainment — page 300: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

CH, XXIJ.] SUMMARY. 2383 what we did under the hypothesis of a solid globe. This then we have accordingly done upon two suppositions, first that the crust beneath the oceans is 20 miles thick, and of the same density as beneath the continents, the oceans being supposed to lie in veritable depressions caused by the greater thinness of the crust beneath them. In that case we find that the radius of the globe, since the inequalities began to be formed, must have been shortened by about 700 miles. This is a much greater shortening than can be supposed possible, and is an additional reason against the hypothesis of the sub-oceanic crust being of the same density as that beneath the continents. In the next place, we suppose compression to have been confined to the continental areas, which is equivalent to attributing the oceans to a denser crust beneath them. We have taken the thickness of the continental crust at the sea level at 25 miles; and in this case we find the shortening of the radius, which would produce the existing inequalities, to be about 42 miles; and then the horizontal compression of the continental areas would average about two per cent. These results confirm the conclusion, that the ocean basins are not caused by depressions, in the upper surface only, of a crust of density everywhere uniform, but that they are due to a greater density, and general depression, of the sub-oceanic crust. XIV. It being certain that a vast amount of water is given off in volcanic eruptions, we next examine the question whether, supposing all the water of the oceans to have been once beneath the crust, it would be possible to obtain a sufficient contraction of the globe to have produced the inequalities, by the trans- ference of this water from beneath to above the crust. But we find that, upon the supposition, the most favourable that we can make, respecting the decrease of volume which the abstraction of this water would impart to the substratum, the hypothesis fails. For the entire remaining portion of the globe beneath the crust would not suffice to afford a sufficient amount of con- traction to have caused the existing continental compression, under circumstances, more favourable than are likely, with COLA @ NOO (CO)