DAVIS. ROCKY MOUNTAIN TERTIARIES. 351 



(751) ; and volcanic ash is said to Lave been ''undoubtedly borne on 

 the winds and deposited in the waters which laid down the several Ter- 

 tiary formations" (761). 



Barbour's account of the Devil's Corkscrew or Da^monelix (Bull. 

 Geol. Soc. Amer., viii, 305-314) reflects the generally accepted lacus- 

 trine origin of the Loup fork beds of Nebraska (Arikaree of Darton, the 

 formation that contains a number of old channels filled with conglom- 

 erate) in certain phrases, such as " on the sandbars of this lake " (307), 

 "plants which drifted into the lake" (312), "the inference from the 

 branching is that the seaweeds or rootlets . . . grew downward in the 

 sand, not upward in the water" (309). 



4. Characteristics of Lake Deposits. — The extracts given above might 

 be greatly multiplied. A review of their sources will show that the 

 explajnation of fresh-water strata as lake deposits has been almost uni- 

 versal among the geologists of our western surveys. The deposits are 

 as a rule well stratified ; they contain no marine fossils ; they frequently 

 preserve an abundant land or fresh-water fauna and tlora. Without 

 explicit discussion of the various conditions under which such deposits 

 could be formed, the earlier observers seem to have taken it for granted 

 that all the fresh-water sediments were gathered in ancient lake basins ; 

 and the later observers have generally followed the belief of their prede- 

 cessors. In a word, stratification has been taken to mean deposition 

 under water and not merely by water. There does not seem to be a 

 single instance, in the accounts of the fresh-water Tertiary formations 

 above referred to, of a deliberate inquiry into the essential characteristics 

 of lacustrine deposits, followed by a comparison between the consequences 

 deduced from the assumed theoretical conditions and the facts deter- 

 mined by observation. In the absence of such an inquiry, it does not 

 seem too much to say that it became habitual to speak of strata bearing 

 fresh-water and land fossils as lake deposits, just as strata bearing marine 

 fossils are habitually spoken of as marine deposits. Under the guidance 

 of this habit of interpretation, it was no more worth while to enter into 

 a deliberate inquiry as to the origin of the so-called lake deposits of 

 Tertiary age than into an inquiry as to the origin of the accepted marine 

 deposits of earlier ages. 



We may now turn to a theoretical consideration of lake deposits, 

 ■without attempting to present anything more than a brief outline of 

 their inferred characteristics. It will not be necessary here to consider 

 small lakes, for those inferred to exist in the Rocky mountain region 

 were scores or hundred of miles in extent; and for the moment, shallow 



