Bulletin of the Geological Society of America . type of deformation which isso rare as to be almost imknown in any other place, Tliis is the develop-ment of boudinage, as it is called by Lohest (figures 2, 3, and 4). THE BOUDINS 651 The Coblencian rocks (Lower Devonian) are composed of quartziteand schist, the quartzite being in beds of from about a foot to about eightfeet in thickness. The quartzite layers appear to have been compressedin the direction of their bedding, with the result that they have beenthickened. The thickening has been distributed in such a way that thebeds have been separ
Bulletin of the Geological Society of America . type of deformation which isso rare as to be almost imknown in any other place, Tliis is the develop-ment of boudinage, as it is called by Lohest (figures 2, 3, and 4). THE BOUDINS 651 The Coblencian rocks (Lower Devonian) are composed of quartziteand schist, the quartzite being in beds of from about a foot to about eightfeet in thickness. The quartzite layers appear to have been compressedin the direction of their bedding, with the result that they have beenthickened. The thickening has been distributed in such a way that thebeds have been separated into a number of parts distinct from one an-other, the parts in cross-section looking like barrels, the ends of whichare separated from neighboring barrels by veins of quartz. In places where quarrying operations have removed the schists fromthe quartzite, one is able to see that the barrel shapes extend into cylin-ders which look like enormous sausages strung out side by side, from ^ I T X ?¥ -T ?I^I 1 I IF? ^ H ak. 1 e a« fe^. S h at Figure 2.—Icealized Bo idinaaen The figure a^ 6^ c, d shows the shape of the rock before it became a boudiu. a h andc d show the maximum shortening. Shortening decreases to nothing at the axes, e eindicate quartz veins. which appearance this type of deformation gets its nama of quartz vein separating each boudin from its neighbor is quite char-acteristic, and the width of spacing between veins is evidently a functionof the width of the bed. The boudins approximate a circle in cross-section. In small beds the circle is small; in large beds the circle is large. The Quartz Veins The quartz veins do not penetrate the schist above and below thesebands of quartzite. They appear to be confined entirely to tlie beds ofquartzite. It is thought by Lohest,^ following Stainier, that these veins ^ M. M. Lohest : Congres Geologicjue International Livret Guide. Excursion Ai!. p. 8. 652 T. T. QUIRKE BOUDINAGE, AN UNUSUAL PHENOMENON wer
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
