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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Geographical Society is collaborating with JSTOR to digitize, preserve and extend access to Geographical Review. HE terms "rock stream" and "rock glacier" have been applied to voluminous tongue-shaped accumulations of rubble and blocks encountered in the mountains of Colorado,1 Wyoming,2 and Alaska3 and in the Alps.' Their scattered occurrence in regions so widely separated suggests a much greater frequency than the published accounts indicate. The presence of rock streams in the Sierra Nevada substantiates this conclusion.The wrinkled surface of the rock streams has challenged the imagination of geomorphologists, who have compared them to lava flows, mudflows, and glaciers. Similarly varied are the interpretations of their origin. They have been explained as glacial moraines,5 as deposits of landslides of the rockfall type,6 as landslide material transported a short distance by small glaciers,7 as the result of creep of landslide deposits,8 as creeping talus,9 and as a special form of denudation associated with dying glaciers;10 and smaller rock streams have also been interpreted as accumulations of talus at the foot of temporary snowbanks.'1 The variety of single interpretations has invited compromise in the form of compound explanations. Sliding of talus over snowbanks, creeping, slumping, and sliding of the regolithic mass, and incipient glacial motion have been combined in one explanation ;12 in another retreat of glaciers has been added to this group of processes ;13 1 Whitman Cross and Ernest Howe: Geography and General Geology of the [Silverton] Quadrangle, [Colorado], U. S. Geol. Survey Geol.

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