Douglass : A Geological Reconnaissance. 255 



alder, poi)]ar, etc. The drainage of the region underwent a change 

 during or after Oligocene times, so that the courses of the rivers were 

 different from what they had been during the Eocene. 



After this there was an increase in the grade of the streams, prob- 

 ably caused by the elevation of the land, the streams cut down into 

 the Lower White River deposits, and again broadened their valleys; 

 this continued until large portions of the White River beds were 

 removed; there were local river and terrestrial deposits, but in Lower 

 Miocene times there was probably more erosion than deposition. In 

 a few places bones of animals were buried. 



In middle and later Miocene times there were considerable deposits 

 made by streams in marshes and lakes. In these were sometimes 

 buried the bones of horses, rhinoceroses, "oreodonts," camels, etc., 

 all different from those found in the White River and Lower Miocene 

 beds, and most of them much larger. Covering some quite large 

 areas are Miocene deposits, composed of disintegrated granite and 

 other rocks, which have not been transported far from their original 

 sources. 



There seems to have been, on the whole, an increase in the grade 

 of the streams from the Oligocene, reaching its culmination at the 

 present time. The present streams have made valleys and ravines in 

 all the Tertiary deposits and have deposited coarse gravel and boulders 

 along the valleys. 



There is not space here to fully give the reasons for the above con- 

 clusions. These are reserved for a more complete treatise on the 

 geology of western Montana v/hich I hope sometime to publish. The 

 above is only the roughest outline, and even if this outline is approxi- 

 mately correct, the details will require many years of patient investi- 

 gation. 



Descending from my bleak elevated position, I "picked up camp " 

 and resumed my journey. I was glad to soon find a road which led 

 to Black Tail Deer Creek, on the most eastern branch of which I 

 reexamined some deposits, in which several years before I bad found 

 remains of mastodons; but this time I was not successful in finding 

 any fossils. The upper beds are late Miocene (Loup Fork) and the 

 underlying beds probably are White River deposits. There are beds 

 of volcanic dust, one of which is very thick. In the afternoon I 

 camped near the house on the ranch of Professor Fenner, who was 

 a teacher in the State Normal School at Dillon, and started to examine 

 the mountains above the ranch. 



