350 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the detailed sections of the High Plateau Tertiaries by Gilbert and 

 Howell (Wheeler's Survey, iii, 157, 267) show the occurrence of numer- 

 ous alternations between shales, sandstones, marls, and limestones. 



Referring to the Tei'tiaries of northwestern Colorado, C. A. White 

 says : — " They were deposited in great lakes, the existence, extent, and 

 elevation of which were respectively determined by the varying configu- 

 ration of the general land surface as elevation and degradation progressed 

 (9th Ann. Rep., U. S. G. S., 695). 



Weed makes brief mention of " the lake whose sediments formed the 

 Livingston beds " in the lower Tertiary of Montana ; and of the gather- 

 ing of " lake waters in the subsidence that caused the deposition of the 

 great thickness of sandstones and clays that form the Crazy mountains " 

 (Bull. 105, U. S. G. S., 27). 



In Clark's " Correlation of the Eocene Deposits of the United States," 

 attention was not especially directed to conditions of deposition ; hence 

 his remarks on this subject may be taken rather as a reflection of general 

 opinion than as a result of direct and independent investigation. They 

 present only conclusions without argument, for example : — " From an 

 open sea of Cretaceous age, in which the life was marine, a gradual 

 change took place to great fresh-water lakes in which the typical Ter- 

 tiary deposits of the Interior were accumulated. . . . The great fresh- 

 water lakes continued with successively dismissed areas during the 

 remainder of the Eocene period. With the advent of the Neocene 

 an extensive area was again covered with fresh-water lakes which 

 finally became drained in the orographic movements accompanying the 

 elevaiiou of the Rocky Mountains" (Bull. 83, U. S. G. S., Ill, 132). 



The Neocene correlation paper by Dall and Harris (Bull. 84, U. S. 

 G. S.) contains many extracts from accounts of the fresh-water Ter- 

 tiaries of the Rocky mountain region, in which frequent references to 

 great lakes seem to be approvingly quoted. As in the preceding paper, 

 the origin of deposits was not the chief subject of the authors' attention 

 in this publication. 



The abundant details concerning the Tertiary formations of Nebraska 

 in Darton's recent report on the " Geology and Water Resources " of the 

 western part of that state (19th Ann. Rep., U. S. G. S.) include mention 

 of local and general unconformities, pebbly beds, cross-bedding, and 

 conglomerate-filled channels. Conditions of origin are hardly touched 

 upon in this report, but two phrases suggest deposition in lakes. A 

 certain soil bed is taken to " indicate that there was here a land sur- 

 face while the Gering formation was being deposited to the south" 



