AMERICAN GEOLOGY SURVEYS UNDER HAYDEN. 



597 



known. The Teton Mountains — a prominent range — were ascended 

 by Stevenson on this trip, this being- the first time, it was claimed, 

 that the feat had been accomplished by a white man. 



Professors Leidv and Cope spent a large part of the summer in 

 studying the ancient lake basins in the interior, and obtained the 

 materials described in Volumes 1 and 2 of the quarto final reports. 

 Lesquereux spent several months in exploring the coal beds to ascer- 

 tain their geological position, and F. B. Meek and H. M. Bannister 

 studied the invertebrates." 



From a preliminary study Lesquereux was inclined to call the lignite 

 beds mostly Eocene. Meek regarded them as Upper Cretaceous, pass- 

 ing through transition beds to the Eocene, and Cope regarded them as 

 Cretaceous. Hayden in this report gives, himself, a brief review of 

 the opinions held and the evidence on Avhich same is based, and con- 

 cluded that the deposition of the lignite strata began during the latter 

 portion of the Cretaceous period and continued on into Tertian" time 

 without any marked physical break, so that 

 many of the Cretaceous types, especially 

 of the yertebrates. may have lingered on 

 through the transition period eyen into the 

 Tertiary epoch. 



In this report Hayden called attention to 

 one feature in the geological structure of 

 the mountains of Montana observed by the 

 survey during the past season for the first 

 time and not noticed in such a marked de- 

 gree in any other portion of the West, and 

 that is the inversion of the sedimentary 

 beds, so that the oldest incline at a greater 

 or less angle on those of more modern ages. 

 As illustrative of this, he gave an east and 

 west section across the Flathead Pass in the East Gallatin range, the 

 central portion of this range being composed of Carboniferous lime- 

 stone standing nearly vertically. A similar illustration of inversion 

 was given by Peale in his report on the geology of Jackass Creek on 

 the upper Missouri River. 



Another point to which Hayden called attention in this report was 

 the fact that the streams "seem to have cut their way directly through 

 the mountain ranges instead of following synclinal depressions," indi- 

 cating, to his mind, that they began the process of erosion at the time 

 of the commencement of the elevation of the surface. (See also Powell, 

 p. 566.) The period of intense volcanic activity manifested in the 

 Yellowstone region he thought to have probably commenced some- 

 where during later Miocene or earl} r Pliocene epochs. 



" Bannister also reported on a geological reconnaissance along the Union Pacific 

 Railroad this same year. 



Fig. 100.— Frank Howe Bradley. 



