. Elements of geology. Geology. PART I. CHAPTER X. 137 Slaty Cleavage. Fig. This disposition of the layers is illustrated in the accompanying diagram, in which I have represented carefully the stratification of a coarse argillaceous schist, which I examined in the Pyrenees, part of which approaches in character to a green and blue roofing Lamination of clay-slate, Montagne de Seguinat, slatC, whilc part is extremely near Gavarnie, in the Pyrenees. quartzOSC, the wholc maSS passing downwards into micaceous schist. The vertical section here exhibited is about three feet in height, and the
. Elements of geology. Geology. PART I. CHAPTER X. 137 Slaty Cleavage. Fig. This disposition of the layers is illustrated in the accompanying diagram, in which I have represented carefully the stratification of a coarse argillaceous schist, which I examined in the Pyrenees, part of which approaches in character to a green and blue roofing Lamination of clay-slate, Montagne de Seguinat, slatC, whilc part is extremely near Gavarnie, in the Pyrenees. quartzOSC, the wholc maSS passing downwards into micaceous schist. The vertical section here exhibited is about three feet in height, and the layers are sometimes so thin that fifty may be counted in the thickness of an inch. Some of them consist of pure quartz. The inference drawn from the phenomena above described, in favour of the aqueous origin of clay-slate and other crys- talline strata, is greatly strengthened by the fact that many of these metamorphic rocks occasionally alternate with, and some- times pass, by intermediate gradations, into rockl of a decidedly mechanical origin, and exhibiting traces of organic remains. The fossiliferous formations, moreover, into which this passage is effected, are by no means invariably of the same age nor of the highest antiquity, as will be afterwards explained. (See Part II.) Stratification of the metamorphic rocks distinct from cleav- age.—The beds into which gneiss, mica-schist, and hypogene limestone divide, exhibit most commonly, like ordinary strata, a want of perfect geometrical parallelism. For this reason, there- fore, in addition to the alternate recurrence of layers of distinct materials, the stratified arrangement of the crystalline rocks cannot be explained away by supposing it to be simply a divi- sional structure like that to which we owe some of the slates used for writing and roofing. Slaty cleavage, as it has been called, has in many cases been produced by the regular depo- sition of thin plates of fine sediment one upon another; but there are many ins
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Keywords: ., bookauthorlyellcharlessir17, bookcentury1800, booksubjectgeology
