452 WALLACE W. ATWOOD 



past season it is known to truncate Wasatch beds. Is it not, 

 however, as late as late Miocene ? Does it correspond in age to 

 the great peneplains of the Grand Canyon district P 1 Are the 

 high-level bowlder-gravels bordering the Front Range of the 

 Rocky Mountains, the Big Horn Mountains, 2 the Livingston 

 Range 3 of the same age as these about the San Juan Mountains ? 

 Do they rest on peneplain surfaces ? Is the Blackfoot Peneplain 

 of Montana described by Bailey Willis 4 of the same age as the 

 one observed in this region ? Are the Wyoming conglomerates 

 about the base of the Uinta Mountains, placed in the Pliocene by 

 the King Survey, 5 of the same origin and age as the high-level 

 bowlder-gravels south of the San Juans ? What is the relation- 

 ship of certain bowlder deposits found near the summit and near 

 the core of the San Juans, and certain ancient stream gravels which 

 have been found by Stone, near the summit of the Front Range, 

 to the bowlder-gravels about the bases of these ranges ? Numer- 

 ous other correlations in the Rocky Mountain areas and in the 

 Pacific Coast mountains are suggested. Has there been with 

 each period of mountain growth in the Cordilleran region of 

 North America a rejuvenation of the streams which affected 

 the headwaters long before it affected the middle courses of 

 the rivers, and did these rejuvenated headwaters distribute 

 the bowlder-gravels in each case on the neighboring pla- 

 teaus? How far were such deposits carried and how were the 

 larger bowlders transported? Numerous cases may be cited 

 where bowlders ten to twelve feet in diameter have traveled at 

 least twenty-five miles from their sources over surfaces of very 

 low gradient. If such bowlders can travel twenty-five miles on 

 gently sloping surfaces, is it not possible for them to travel much 

 farther than that over low gradients ? How are huge bowlders 

 transported over nearly horizontal surfaces ? How far have 

 climatic changes affected the work of streams in the Rocky Moun- 

 tain region ? Are the reported glacial deposits in southeastern 



1 H. H. Robinson, Am. Jour. Sci., 4th Series (1907), XXIV, 109-29. 



2 Salisbury and Blackwelder, Jour. Geol., II (1903), 220-23. 



3 Bailey Willis, Bull. Geol. Soc. Am., XIII (1902), 329-30. 



4 Op. cit., 310. 



s Hague and Emmons, Rep. of 40th Parallel Survey (1877), II, 64-65, 188-89 ff. 



