OF THE WHITE KIVER BEDS OF MONTANA. 



239 



Avon some bone fragments were found, which confirmed the belief that these beds are 

 Oligocene. 



After crossing a basaltic lava flow south of Avon the Tertiary beds appear again, but 

 the fossils obtained here, as previously stated, are of later date, being cither Miocene or 

 Pliocene. Continuing my course southward I found that south of Silver Bow, as had 

 been mistrusted, the lake bed deposits were continuous across the main divide. It is evi- 

 dent that previous to Miocene times a river had carved out a broad valley across what is 

 now the watershed that divides the waters of the Atlantic from those of the Pacific ; so 

 the divide then occupied a different position from what it does now. In Tertiary times, 

 probably by the formation of a great lake, this valley was partly filled with sediment, 

 and after the drying up of the lake the drainage was changed. It is very probable that 

 at some time during the Tertiary a lake extended from the northern part of the Deer 

 Lodge valley southward to the Big Hole, eastward to the Jefferson, then northeastward 

 to the Missouri river and down the Missouri to the region of Helena, a distance of 180 

 miles. There is no barrier and it is evident that there was none, and the Tertiary 

 deposits can be traced the greater portion of the way. This, of course, may have happened 

 more than once. A little south of the divide, on Divide creek, part of the skull and 

 skeleton of a small horse was obtained. 



There are only three regions from which fossils have been secured sufficiently 

 abundant, and characteristic, so that it can be positively stated now that the strata are 

 White Eiver; but there are other regions that are only a little doubtful. I believe that 

 the White River, like the Loup Fork, occurs in all the principal valleys of southwestern 

 Montana,. 



There is some doubt concerning the John Day. The lower Deep River beds near 

 White Sulphur Springs appear to belong to that age (Scott, 1893), and some fossils in 

 my collection, especially those obtained east of Drummond, appear to be more like John 

 Day than White River, but there are not enough to settle the question. 



The three regions that are certainly While; River are : (1) on Pipestone 

 creek, (2) on Thompson creek northwest of Three Forks, and (3) northeast of Toston 

 near Cottonwood creek. Those on Black tail Deer creek are probably White River. For 

 convenience, until the strata in the different localities are satisfactorily correlated, I will 

 give them local names. 



White River Oligocene. 



Pipestone Beds. 



These are on Pipestone creek at two localities, one on the Big Pipestone near Pipestone 

 Springs and the other on a branch, the Little Pipestone, The first is north of west and 



