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Published October 1940 | Published
Journal Article Open

Fluting and Faceting of Rock Fragments

Abstract

Rock surfaces are eroded by particle-laden currents of air and water so that under given conditions polishing, grooving, and fluting result. Polish is characteristic when the particles are fine and when abrasion predominates over solution in removal of material. Grooving and fluting in homogeneous rocks are caused by the more or less regular variation in abrasive intensity resulting from vortical movement of the fluid. When the vortices are shed from points of separation of flow from the rock surface, it seems that grooves elongate in the current direction may be cut. Under some conditions the vortices appear to be fixed in position and discontinuous flutes are cut. The stream flutes and wind flutes which have been observed are similar in form although the stream flutes are between fifteen and twenty times larger. Under certain conditions fragments are faceted in particle-laden currents. Facets at high angles toward the current tend to be worn off uniformly and polished, while those inclined at low angles are cut by the most characteristic flutes and grooves. Limestone fragments partially imbedded in alluvium may be faceted by solution during rain wash. Moisture driven by rain commonly produces solution effects consisting of an anastomosing and rugose system of ridges and rills on nearly horizontal surfaces and of deflected streamlike rills on steep-side and lee surfaces. In erosion of limestone fragments by particle-laden air currents abrasion is dominant over solution. Rilled surfaces tend to be smoothed and polished. However, it is believed that all the various types of polish, fluting, grooving, faceting, and rilling may develop essentially simultaneously in one locality, presumably during the time span of a few tens of years The predominance of one feature or another depends upon the idiosyncrasies of the immediate neighborhood of the limestone fragment.

Additional Information

© 1940 University of Chicago Press. The field work in the Grand Canyon district was carried out in conjunction with studies of the Archean rocks, a geological project, supported by the Carnegie Institution of Washington. The field work in the Death Valley region was supported by a grant from research funds by the California Institute of Technology. The writer wishes to thank Professor Kirk Bryan for many valuable suggestions and for criticism of the manuscript.

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Created:
August 19, 2023
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October 23, 2023