Earth's crust

“ For untold millions of years the rocks at and near the earth’s surface have been crumbling; streams have been incessantly sawing into the lands; the sea has been eating into continental masses; the winds have been sculpturing desert lands; and, more intermittently and locally, glaciers have plowed through mountain valleys, and even great sheets of ice have spread over considerable portions of continents. Throughout geologic time, the crust of the earth has shown marked instability. ”

“ If the earth had a cool thin crust upon a hot fluid interior, and that thin crust were able to sustain itself during geologic ages so that the shrinkage should accumulate within, until finally collapse came, giving an era of uplift, it is obvious that we could account for such cycles. There is very clear evidence that the outermost layer of the earth's crust is but a thin shell like the outer shuck or exocarp of a butternut, so thin that it is not at all possible that it can sustain itself for more than a hundred miles or so, or for more than a very few years at the outside. ”

“ A large portion of the earth’s crust consists of such materials as sandstones, limestones, shales, and similar strata which have been formed in precisely the same manner as deposits are being accumulated at the present day. The whole surface of the earth is continually exposed to the action of destructive agencies, and suffers perpetual decay ”

“ In any case, the earth is hot inside as proved by deep well records and igneous phenomena in general, and it is a contracting or shrinking body as proved by the many large scale zones of wrinkling or folding of rocks. If, then, highly heated solid rocks at reasonable distances down in any part of the earth are subjected to relief of pressure by an earth movement such as upward crumpling of the crust, or by readjustment of large fault blocks, such heated solid rocks would become molten. ”

“ As to the crustal movement whose tendency is to spill the waters westward out of the Erie basin, we may observe that the earth's crust is most uneasy and its movements most uncertain. Nearly every place is going either up or down, few are in a state of actual quietude. ”

“ At the conclusion of the Wealden period, the crust of our globe underwent another great change. The fresh-water rocks we have just been studying were probably submerged by some violent subterranean or subaquean agency, and upon a great part of them a new deposit was gradually formed. Foot by foot, and inch by inch, slowly accumulated those cretaceous particles (Lat. creta, chalk) which now constitute the chalk hills and cliffs of our own country, to say nothing of the extent of territory in Europe occupied by this well-known mineral. ”

“ No one who has not studied the crushed, crumpled, fractured, and altered condition of many of the sedimentary rocks of the globe, can form the faintest idea of the enormous effects of the internal forces which have been in operation within the earth's crust during earlier geological periods. ”

“ The wrinkles of our clothing are often better illustrations of rock-folds than the models and diagrams used for that purpose. This becomes self-evident when we reflect that the earth’s crust is exceedingly heterogeneous in composition and structure, and must, therefore, yield unequally to the unequal strains imposed upon it. ”

“ The great lesson taught by the study of the outer crust is that the earth mother, like her children, has attained her present form through ceaseless change, which marks the pulse of life and which shall cease only when her internal forces slumber and the cloudy air and surf-bound ocean no more are moving garments. ”

“ If the earth were liquid within and merely crusted over by a shell of rock of moderate thickness, it would yield appreciably to tidal stresses, and this yielding would change the capacity of the interior so that with every distortion of the spheroid a portion of its fluid interior would be forced to the outside, and with every return to the more spheroidal form there would either be a re-flow to the interior or a shrinking of the crust. ”

“ Certainly our machine had risen easily enough through the purple rocks below us. The scientific aspects of that second crust about the earth have been considered very carefully, and the best scientific opinions have been sought.
Mankind dwells upon a comparatively thin crust about the molten or plastic interior of the earth. It would seem there is a similar crust about the air. Science long ago had evidence of it in the reflection of radio waves by the so-called Heaviside Layer. ”

“ We can not include as the earth's crust the surface of the earth on which we live, and which consists of loose materials disintegrated by weathering, breaking, and numerous causes, but the solid crust, often lying at a considerable distance beneath us, which bears these materials, and from which the spherical waves emerge. ”

“ In the present state of our knowledge, we can explain such appearances only by supposing that the heated materials within the earth's crust poured out frequently, meeting little resistance,—that they then scattered and were precipitated in the ocean around, settling in successive strata at its bottom,—that through such strata the heated masses within continued to pour again and again, forming for themselves the chimney-like outlets above mentioned. ”

“ During the short span of the ordinary human life weathering effects are generally of very little consequence, but during the long ages of geologic time the various processes of weathering have been slowly and ceaselessly at work upon the outer crust of the earth, and such tremendous quantities of rock material have been broken up that the lands of the earth have everywhere been profoundly affected. ”

“ But it may be argued that all kinds of terrestrial energy are growing feeble, that the most active denudation now in progress is much less vigorous than that of bygone ages, and hence that the stratified part of [Pg 189] the earth's crust may have been put together in a much briefer space of time than modern events might lead us to suppose. ”

“ Is it then assuming too much to infer, that they are in fact the crust which has been first formed upon the surface of the earth, intensely heated by its own condensation, under the action of the gravitating force, that, communicated to it by the hand of the Creator, determined its figure, and still maintains its equilibrium. ”