PHYSIOGRAPHIC STUDIES IN SAN JUAN DISTRICT 453 



Utah, 1 in which there are granitic and gneissic bowlders one to 

 five feet in diameter, the origin of which is at present unknown 

 unless it be the San Juan Mountains, true glacial deposits or stream 

 deposits ? Could mountain glaciers from the San Juan Range 

 have reached southwestward one hundred miles from the base 

 of the range ? Is there not some other explanation for the coarse 

 bowlder deposits reported in that portion of the plateau district ? 2 

 Has there been a continuous or periodic growth of the San Juan 

 dome during late Tertiary and Quaternary times ? 3 How are the 

 great systems of fissures which cut the late Tertiary volcanics 

 related in age to the recent deformative movements ? Co-operative 

 work by all who are engaged in field studies in the Rocky Mountains 

 and plateau provinces should prove of great value in promoting 

 the solution of these problems. 



1 D. D. Sterrett, U.S. Geol. Survey, Mineral Resources (1908), Pt. II, 825 (1909). 



2 W. M. Davis, Proc. Am. Acad. Arts and Set., XXXV (1900), 345-73. 



3 Cross and Spencer, U.S. Geol. Survey 21st Ann. Rep. (1900), Pt. II, 100. 



