We were well into the 19th century before scientists realized that vast parts of Europe and North America had been covered by thick layers of ice in the geologic past. The evidence included so-called erratics, boulders far from any possible source, and moraines—ridges left as debris carried by glaciers accumulated around the melting edges. Other evidence was in the form of bedrock, polished and grooved by the passage of ice and embedded rocks, gravel, and silt.
If you clamber around on the southwestern slopes of the Franklin
Mountains, you may be startled to see slick surfaces looking for the world like those
created by the great ice sheets. A continental ice cap covering the northern Chihuahuan
Desert? Not quite. Glaciers aren't the only things that leave slick surfaces as
they grind across bedrock. In the case of the Franklins, as in some other places in the
Southwest, the polisher was not a towering layer of ice, but part of the mountain
itself—a landslide block, sliding downslope by the power of gravity, surely as awesome
as any overgrown ice cube.
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.