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Desert Diary


Many people enjoy collecting small, hard stones and bringing out their beauty by polishing them. The usual method of polishing a number at the same time is to place them into a specially made tumbler. This machine consists of an electric motor that rotates a drum. At each turn, the rocks within cascade down the inside surface of the drum, striking one another and knocking off tiny bits. After many hours, angular projections and rough spots are worn away, leaving smooth, polished gems—in beauty, if not in monetary value.

The process mimics nature, as so many man-conceived ideas do. Smooth, rounded rocks have always been recognized as the work of rivers or seashores. Rivers aren't the only source in the Southwest, though. In northern Chihuahua, springs once were active near ice-age lakes. The roiling waters of these springs polished not only gravel, but also the bones and teeth of animals that met their demise at the edge of a spring. Entombed in rock as the springs went extinct, these polished fossils lend a macabre beauty to the silent earth.
pen and ink

Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.


Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.

spring deposit sample with teeth

Consolidated spring deposit with fossil teeth. The tooth labeled "Equus" is a lower tooth of an extinct horse displayed in cross section due to breakage during excavation. The three ridges labeled as "Mammuthus" are a small part of a mammoth molar; the yellowish portions are unbroken surfaces that have been highly polished by the tumbling action of the spring. The matrix is primarily of cemented small pebbles. Photograph of Centennial Museum specimen by A.H. Harris.



Comadurán, O., D. A. Giles, D. V. LeMone, A. H. Harris, and S. Fitzpatrick. 1992. New mammoth fossil locality discovered near Villa Ahumada, Chihuahua. Pp. 107-110, in Geology and mineral resources of northern Sierra Madre Occidental, Mexico (K. F. Clark, J. Roldán Quintana, and R. H. Schmidt, eds.). El Paso Geological Society, Guidebook, 1992 Field Conference.