148 Annals of the Carnegie Museum. 



found what one could be sure were old lake terraces. But this does 

 not appear to be any evidence of the absence of lakes, for in a region 

 of comparatively rapid erosion, we could hardly expect them to endure 

 so long. 



Fossil plants were collected in several places in the White River 

 during the last summer. In one locality in the Lower Madison 

 Valley tracks of birds were found on the sandstone. Just above were 

 beds of pure volcanic ash beautifully ripple-marked. 



The lower division of the White River — the Titanotherium Beds — 

 east of Winston and southeast of Helena, attain a considerable thick- 

 ness. One measurement gave 4500 feet, another farther south 4900 

 feet. Where this latter measurement was made a fault occurs, the 

 exact displacement of which was not ascertained and it is possible that 

 this might bring this measurement a little nearer to the former one. 

 The beds vary from nearly horizontal to a dip of 53°. These measure- 

 ments do not include the whole thickness of the White River here. 

 The Missouri Valley makes a gap of a couple of miles and when seen 

 again across the river the strata are nearly horizontal and have changed 

 in character. About 150 feet of strata are exposed here. Adding 

 this to the 4900 feet we have here a measurable thickness of 5050. 

 How much is lost by the erosion of the river valley it is not possible 

 to tell. The upper beds here are like the lower ones exposed on the 

 Madison River. Above the latter, on the Madison, I measured 300 

 feet of mostly fine, stratified deposit. 



There is a possibility that the lowermost of these beds may extend 

 down into the Eocene, though there is at present no evidence of this. 



At some time, either previous to or succeeding the White River 

 epoch, the rivers of western Montana underwent much change, for in 

 many places they leave the older valleys which were filled, or partly 

 filled, with Tertiary deposits and flow through deep narrow canons in 

 the Archaean and Palaeozoic rocks. About ten miles below Whitehall 

 the Jefferson flows eastward through a long canon, while both north 

 and south are old valleys containing only Tertiary or later deposits. 

 In many places the streams have left what seems to be their easy, 

 natural course and made their difficult way through old granite, lime- 

 stone, and quartzite rocks. 



The beds in the vicinity of Helena contain much sand and coarser 

 material, waterworn gravel brought from a distance, and unworn 

 angular fragments from the adjacent Algonkian slates and quartzites. 



