Page:Popular Science Monthly Volume 17.djvu/212

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M. A. DAUBRÉE, in his recently published "Études Synthétiques de Géologie Expérimentale" (Synthetic Studies in Experimental Geology), besides giving the results of studies on the formation of meteorites and on the production of the chemical and physical phenomena of geology, describes a series of interesting and instructive experiments upon the manner in which the mechanical operations of which the earth's strata bear witness were brought about.

M. Daubrée began this series of experiments with an investigation of the processes by which the convolutions of the stratified beds were produced. With a very simple apparatus, a frame of iron strengthened by long screws crossing two of its contiguous sides, he subjected flexible laminæ, as representing in miniature the strata of the globe, to pressures of varying energy and direction. Under these constantly measuredPSM V17 D212 Geology fracture demonstration using plates of glass.jpgFig. 1.—Double system of conjugate fractures developed in a plate of glass, GG, by the effect of the torsion produced by the turning-handle, TT. EE, block of wood in which the other end of the glass plate is fastened.(One sixth the natural size.) efforts he saw reproduced all the characteristic traits of the geology of regions whose strata are warped, synclinal valleys, anticlinal crests, slopes, and reversals of strata, strata in the form of C, strata in the form of S, etc.

Prosecuting his experiments beyond the limits of the elasticity of bent laminæ, M. Daubrée went into the investigation of the origin and mode of formation of terrestrial fractures. He was able by means of his new processes to produce imitations of joints and faults in all their details. An unforeseen result of his experiments was, that they disclosed evidences of mutual coordination between natural fractures which observation alone had failed to notice. This point deserves a careful examination. A rectangular plate of glass, GG (Fig. 1), was clamped between two jaws of wood tightly bound by screws so as to form a kind of vice, EE. The other end of the plate was fitted to a wrench, TT. By turning the wrench around horizontally, M. Daubrée twisted the plate of glass so that it speedily broke into a thousand pieces. Having previously taken care to paste a sheet of