Douglass : A Geological Reconnaissance. 251 



geological stages, extend, or previous to erosion, did extend continu- 

 ously over all the valleys in the region of the head-waters of the 

 Missouri River, and covered nearly everything, except the higher 

 mountains. 



It is possible, however, that the large area of eruptive rock, through 

 which the Missouri River has cut a canon from near Wolf Creek to 

 Cascade, may have formed a barrier sometime during the Oligocene ; 

 but this supposition, like that of other imagined barriers, may not 

 bear the light of investigation. It is possible, however, that there 

 were some isolated valleys. No connection between the Tertiary de- 

 posits in the Bitter Root and Missoula valleys with other valleys has 

 yet been traced ; but the deposits which occupy them seem to be prin- 

 cipally composed of sediments carried by streams, the products of 

 sheet-erosion, and rocks decomposed /;/ situ. 



From Logan to Virginia City, Montana. 



At Logan we hired a team of cayuses and a spring-wagon and drove 

 to the region northwest of Three Forks, where I had previously col- 

 lected Devonian fossils. Here we camped for a few days and made a 

 fine collection of fossils from the Upper Devonian shales, part of the 

 fauna of which, according to Mr. Raymond, "seems to be much more 

 like that of the Upper Devonian of South Devon, the Rheinland, and 

 other localities in Europe and Asia, where the top of the Devonian is 

 indicated by one containing numerous species of Clymenia and Goni- 

 atites.''^^ In this region are many small exposures of the White 

 River Tertiary beds, and a few fragments of bones of mammals were 

 found. 



From this place we struck westward. The next camping place was 

 at an exposure of the Lower White River beds south of Pipestone 

 Springs on Little Pipestone Creek west of Whitehall, where in 1899 I 

 had collected the remains of small mammals. A few interesting speci- 

 mens were found here, among which were portions of the jaws of un- 

 known insectivores and marsupials (?), and a portion of the skeleton 

 of an oreodont (merycoidodont) about the size of Merycoidodon ciil- 

 bertsoni. The merycoidodonts previously described from these beds are 

 all much smaller. 



The next important stop was on the Ruby River near Laurin. 



■'"Oil the Occurrence in the Rocky Mountains of an Upper Devonian Fauna with 

 Clymeniti.^' Amer, Jour. Sci., Vol. XXIII, Feb., 1907. 



