Penny Blood: Serial Sensation and Working-Class Entertainment — page 60: what you’re looking at

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

CH. IV. | LATERAL PRESSURE, ITS AMOUNT. 43 propagated downwards as far as the causes which tend to pro- duce them are felt. — ree Let us now return to the consideration of /the external «'’’ ; layers of rock, supposed to consist to the depth whinh]vr FS, . os acquainted with them chiefly of sedimentary stra. ~**ol 7D Y It has been shown that if an external layer we " supppned., eth. for a moment to be unsupported from beneath, it would be acta: + **” upon horizontally in any two directions at right angles to each other, by pressures which, upon a given area of section, would be equal to the weight of a column of rock of the same sectional area, and of the length of half the earth’s radius. We may admit then that the crumpling by lateral pressure, which is such a common phenomenon among rocks of all ages, and especially among the older rocks, 1s due to the force, whose amount has here been approximately calculated. Wherever from any local weakness the superficial strata have been dis- posed to yield, they will have formed a ridge, or a series of ridges; and the pressures at any point being resolvable hori- zontally into two at right angles to one another, which can in no way neutralize each other, the chains of mountains which traverse a country, if of equable elevation, may @ priort be expected to form a network, or if there be one great master chain, like the Andes, it may be expected to be supplemented by a number of smaller chains at right angles to it, the amount of relief which has been afforded by the great chain in one or two great, folds, being equal to the sum of what has been afforded in the perpendicular direction by the lesser chains in many lesser folds. A semi-lunar arrangement of a chain would give relief in both directions at once. But whether the for- mation of a chain of mountains in this manner is compatible with a solid globe 1s doubtful. To take an instance of the mode of action of lateral pressure we may refer to a very instructive comparison between the Alps and Himalayas which has been made by Mr Medlicott, and pub- lished in the Journal of the Geological Society’. He there shows that the reversed apparent faulting by which the older rocks of the central chain of the Himalayas appear to overlap 1 “Jour. Geol, Soc.,” Vol. xxiv. p. 34. COMiCOOokxS.conn