14(3 Annals of the Carnegie Museum. 



Fossils were found in only a restricted locality. The hill where 

 Heptodon ? and the jaws of Hyrachyus ? were found is composed of 

 stratified material, and it contains quartz geodes, tubes lined with 

 crystals both of calcite and quartz, and calcified trunks and twigs of 

 trees. 



It is hoped that these beds will soon be more fully and carefully 

 explored. 



List of Species. 



Heptodon ? 



Hyrachyus priscus Douglass. 



Hyrachyus ? 



Aletamynodon ? 



OLIGOCENE. 



The White River Formation. 



That a great part of the White River deposits of Montana was 

 formed in water is evident. It does not appear that the water was, as 

 a rule, very deep. There are undoubtedly not only lake, but marsh 

 and river deposits. The evidence points to some slow acting obstruc- 

 tion of the water, rather than to a more sudden appearance of high 

 barriers making deep lakes which were in course of time gradually 

 drained by the cutting of a channel through the barriers. The con- 

 ditions could be better explained by supposing that there was slow 

 and inconstant upheavals or oscillations across the path of drainage. 

 When the rate of elevation of the barrier was greater than the rate of 

 deepening of the channel through it, there would be ponding of the 

 water. The excess of erosion would, if it operated long enough, 

 lower the water level, thus making dry and marshland where water 

 had been before. So in the long time in which there was an unequal 

 rate of raising of the barrier the conditions would be very complex. 

 The relation between the rate of elevation of the barrier, sedimenta- 

 tion, and erosion of the channel were such that the water of the lakes 

 was not usually of great depth. There are undoubtedly not only 

 lake, but nearly all kinds of fresh water deposits as we should expect 

 under such conditions. 



This is only a hypothesis which remains to be proven or disproven, 

 but which at the present time seems to the writer to best accord with 

 the data at hand. 



We find nearly everywhere evidences of shallow water, such as rip- 

 ple marks, bird tracks, plant remains, shallow water mollusca, etc. 



