Penny Blood: Serial Sensation and Working-Class Entertainment — page 203: what you’re looking at

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

186 COMPRESSION AND VOLCANIC ACTION. [cu. xv. that region, and cause compression, by drawing the neighbouring parts towards itself. But the discussion of the attraction of mountain masses by Sir G. B. Airy, quoted in the eleventh chapter, suffices to show that such a supposition would be erro- neous. Indeed it is easy to see that, when a column floats vertically in a heavier fluid, the horizontal attraction upon a particle, at or near the surface of the fluid, will be somewhat less for a longer than for a shorter column. It is not possible therefore that the cause of compression can be explained by the attraction of the thickened crust upon the neighbouring parts. To guide us in this new branch of enquiry, let us enquire whether any geological appearances in the crust itself can give a key to the cause of compression. When we examine any district where considerable sections of metamorphosed strata are exposed, we are struck with the abundance of dykes of intrusive rocks, which permeate them*, These are commonly, though not always, more or less vertical in position. Likewise in any section, carried across an extensive range of country, large and wide dykes are ‘laid down, sometimes as actually determined by the surveyors, and sometimes as the supposed channels, through which over- lying sheets of igneous rock have been raised to the surface. What have been the conditions under which these intrusive more or less vertical sheets of matter have found their way into the positions in which we see them? That they have come up from below no one doubts; but what has been the force that has injected them? How have the chasms originated which they occupy? If the separation of their walls has been effected by any pressure acting within the chasms themselves, then we have an indication of the existence of some force tending to compress the crust. | Upon the hypothesis that a crust of about 25 miles thickness rests upon a fluid substratum of highly heated rocky matter in a state of igneo-aqueous fusion, let us suppose that a crack is 1 Prof. Liveing, from an estimate by the eye alone, made at my request in the Channel Islands, thinks that the horizontal area occupied in the cliffs of Guernsey and Serk by intrusive dykes cannot be less than from 2 to 3 per cent. of the whole area. Jersey consists largely of volcanic products. eomichooks @ (CO)