602 PROCEEDINGS OF THE WASHINGTON MEETING 



survey, but a reconnaissance, and as such their results would necessarily be subject 

 to modification by more detailed work, especially when done in the lightof modern 

 advances in geological and geographical knowledge. They had hoped that long 

 before this these Tertiary deposits would have been made the object of special 

 geological studies, for there were; many facts with regard to them that could not be 

 Satisfactorily determined in these hasty and, as regards their actual area, very im- 

 perfect observations; yet I can hardly feel willing to admit that such polemic 

 statements as those made by Professor Davis, where not based on any new observa- 

 tions, cast any doubt on the correctness of their conclusions with regard to these 

 deposits. With the exception of those on the Great plains east of the Rocky 

 mountains, the Tertiary lake deposits there noted occur in basins still enclosed 

 within mountain ranges where no considerable tluviatile action is conceivable. In 

 all, the character of bedding and nature of successive beds is such as to necessitate 

 their having been deposited in still waters. 



In the case of the Vermilion creek (Wahsatch) beds cited by Professor Davis, 

 the great thickness of conglomerates mentioned is found in the southwest corner 

 of the Green River basin, in the right angle formed by the lofty Wahsatch and 

 Uintah ranges, and was evidently washed down rapidly from the then even steeper 

 slopes of these ranges and spread out along the shoreline of the lake. What its 

 exact relations to the shore were, and whether it represented the shoreline phase 

 only of the lower or Vermilion Creek series, or of the overlying Green River and 

 Bridger series as well, we had not the time to determine. Toward the center o* 

 the basin the beds of all the series become so thinly, uniformly, and evenly bedded 

 as to preclude the possibility of fluviatile deposition, especially as they were formed 

 in what is now, as well as could be determined, an enclosed basin without outlet. 



Something in the nature of Professor Davis' fluviatile origin was suggested by 

 me for the latest phase of deposition in this region for what I called the Wyoming 

 conglomerate (Bishop Mountain conglomerate of Powell), which was spread out 

 over the flanks of the Uintah range in a sort of sheet-flood deposit without stratifi- 

 cation, but which left no fine grained representatives toward the middle of the 

 basin. A similar origin to this is also conceivable for some of the coarser beds on 

 the eastern flanks of the Rocky mountains, and a fluvio-lacustrine origin was sug- 

 gested by me as one of the possibilities of the loess of the Denver basin. As for 

 the Denver and Arrapahoe beds, I will resign the floor to Mr Cross, who is more 

 intimately acquainted with them by personal observation. 



Mr Whitman Cross said in substance the following : 



Since the abstract of Professor Davis' paper, which we have heard, deals only 

 with general principles, and did not contain special references to the formations 

 whose origin he questions, I can not directly discuss the points he may raise as to 

 the origin of the Arapahoe and Denver beds. In general, however, the hypothesis 

 of a fluviatile origin for them must explain many facts besides those evident from 

 the texture and composition of the strata. Since these formations were first dis- 

 covered numerous other formations of the same lithologic character, the same 

 details of texture, and in several cases shown to be of the same age by fossil re- 

 mains, have been found in various parts of Colorado, namely, in South park, some 

 50 miles southwest of Denver; in Middle and North parks, to the northwest of 

 Denver; at Canyon City; on the Animas river south of the San Juan mountains, 



