354 PROCEEDINGS OF THE AMERICAN ACADEMY. 



great lake" in which "the accumulation of fine sediment . . . went on 

 with but slight changes for a sufficient length of time for more than a 

 thousand feet of evenly bedded strata to be laid down one above an- 

 other " (Bull. 108, U. S. G. S., 22, 23). 



It is evident from such examples as these that certain western Ter- 

 tiary deposits have a well characterized lacustrine facies : but it is also 

 evident that just in so far as Tertiary lakes are inferred from the occur- 

 rence of fine and uniform sediments, they are excluded by the occurrence 

 of coarse and variable sediments. It must be concluded that the lakes, 

 whose quiet waters permitted the accumulation of fine-textured, tliin- 

 bedded shales, had disappeared when the deposition of cross-bedded con- 

 glomerates began. It is possible that some variation of lacustrine con- 

 ditions may have been tacitly assumed by the writers of the survey 

 reports. It may have been taken for granted that subordinate varia- 

 tions of shore line and depth were produced by orographic movements 

 during the existence of each great Tertiary lake, sufficient to have 

 caused slight changes in the bottom deposits, but not sufficient to have 

 produced significant unconformities in the accumulated strata ; or it 

 may have been intended that some small share of the deposits were laid 

 down outside of the margin or above the level of the lake waters ; but 

 it would be going beyond the spirit as well as beyond the letter of the 

 reports above quoted to give a considerable value to deposits of subaerial 

 origin, resulting from alternations of land and lake conditions, in any of 

 the western Tertiary formations. "When a student reads these reports, 

 he will without question conclude that their authors regarded subaerial 

 deposits as of negligible volume because no mention is made of them, 

 and that the formations are essentially lacustrine because continual 

 mention is made of deposition in large lakes. 



Reference will be made again to fine-textured deposits on a later page; 

 attention being now turned to special examples of coarse-textured and 

 variable strata such as are repeatedly described in the accounts of our 

 western " lake deposits." 



5. The Vermillion Greek Beds of Wyoming. — Many authors might be 

 quoted to show how frequently various kinds of deposits in addition to 

 those of fine texture and even bedding occur in formations that are 

 described as lacustrine ; but in this section extracts will be made only 

 from King's account of the Vermillion creek (lower Eocene) beds in the 

 Green river basin, enclosed page numbers again referring to the first 

 volume of the Fortieth Parallel Survey reports. The strata that are 

 found at some distance from the inferred " shore-line of the lake," and 



