BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 17, PP. 317-320, PLS. 40-42 JULY 27, 1906 



MOULIN WOKK UNDER GLACIERS* 



BY G. K. GILBERT 



(Read before the Gordilleran Section of the Society December 30, 1905) 



CONTENTS 



Page 



Statement of the problem studied 317 



Origin of the rock sculpture 317 



The moulin, or glacial mill 318 



Explanation of plates 320 



Statement of the Problem studied 



In glaciated regions I have several times encountered an aberrant and 

 puzzling type of sculpture. Inclined surfaces, so situated that they can 

 not have been subjected to postglacial stream scour, are sometimes carved 

 in a succession of shallow, spoon-shaped hollows, and at the same time are 

 highly polished. They resemble to a certain extent the surfaces some- 

 times wrought by glaciers on well- jointed rocks, where the hackly charac- 

 ter produced by the removal of angular blocks is modified by abrasion; 

 but they are essentially different. Instead of having the salient elements 

 well rounded and the reentrant angular, they have reentrants well rounded 

 and salients more or less angular; and they are further distinguished by 

 the absence of glacial striae. 



An example appears in the foreground of plate 40, representing the 

 canyon of the South fork of the San Joaquin river, in the heart of the 

 glaciated zone of the Sierra Nevada. The peculiarly sculptured spot is 

 •high above the river. 



Origin of the Eock Sculpture 



The key to the puzzle was found on a dome of granite standing at the 

 southwest edge of Tuolumne meadow, Sierra Nevada, just north of the 

 Tioga road. The dome is several hundred feet high and in general is 



♦Published by permission of the Director of the U. S. Geological Survey. 



XXIX— Bull. Geol. Soc. Am., Vol. 17, 1905. (317) 



