Penny Blood: Serial Sensation and Working-Class Entertainment — page 192: what you’re looking at

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

CH. XIII] AMOUNT OF COMPRESSION. 175 Consequently, any thickening from sedimentation is not included in &; for that will be derived from matter elevated by compres- sion. %(A’) and = (B’) are the volumes of the elevations and depressions above and below the upper mean level of this crust; the position of the crust as a whole being affected by the lateral flow of the subjacent fluid, through the intrusion into it of the downward protuberance of the mountain roots. This is allowed for in the equation. as if the fluid were a perfect fluid. If we assign to o the value infinity in this expression it ought to reduce to the datum-level equation, for in that case there would be no downward protuberances, and therefore the mean level of the crust would not be altered from the datum- level, because there would be no flow of fluid beneath it. Now this it does, for when o = o the equation becomes 8rrke = 3 (A’) —>% (B), which is the datum-level equation. It is self-evident that it will be quite impracticable to arrive at anything approaching to an accurate estimate for &(A’)—%(B’, because, in the first place, we can only guess at the position of the mean level; and secondly, we can only roughly estimate the amounts of %(A’) and =(B’) respectively. Nevertheless it will appear that we may draw important conclusions even from such guesses as we can form. Referring to Atlases' which have been published since the voyage of the Challenger, we find the oceanic area divided into five portions, whose mean depths are taken to be, (1) from 1 to 2 miles, (2) from 2 to 3 miles, | (3) from 3 to 4 miles, (=8), (4) from 4 to 5 miles, (5) above 5 miles. The first may be taken as extensions of the elevations which have produced the continents, The second, where not connected 1 For example, ‘‘Letts’s popular Atlas” maps 3 and 4. See also * Thalassa” by J. J. Wild, Ch, 1. Marcus Ward, 1877. GONG oOo SS (CO)