254 Annals of the Carnegie Museum. 



times occurring on mountain ranges seven thousand or eight thousand 

 feet above sea level. Although the deposits are not all of the same 

 age, this does not change the truths taught by the topography of the 

 country. The history of these modern deposits is so complex, that its 

 study has never been carried out into details, but o;jr present knowl- 

 edge points to the following partial outline of events as the most 

 rational that we are able at the present time to construct. 



In later Cretaceous and early Eocene times there had been up- 

 heavals and erosion of the land. This region was considerably ele- 

 vated, and probably, in part at least, rugged and mountainous, traversed 

 by swift-flowing streams. During the Eocene the streams reached their 

 base-level of erosion and broadened their valleys. These conditions 

 must have continued for an immense period of time reducing a large 

 portion of the region to a plain. The streams became sluggish and 

 drainage was obstructed, probably in part by accumulation of sedi- 

 ment and by volcanic dust which was wafted from no one knows ex- 

 actly where. Ponds, marshes, and lakes were formed. Into these 

 dust was carried by wind and water, depositing nearly white sediment, 

 layer on layer, and thick masses of unstratified material. Probably 

 unusually heavy precipitations caused the overflow of flood-plains, 

 and deposition and rearrangement of sediment. Evidently these 

 conditions existed for a great length of time, for the sediments are 

 in some places thousands of feet in thickness. During portions of 

 this immense lapse of time arid conditions prevailed. There were 

 lakes without outlets, and evaporation of the waters caused gypsum and 

 other minerals to be deposited. In some places fish and water-snails 

 were imbedded in the sediments, and in other places remains of rhino- 

 ceroses, little three-toed horses, tapir-like animals, rodents, insectivores, 

 huge titanotheres, and other animals unlike anything now living on 

 the earth, were buried. This was the oldest White River (Oligocene) 

 Period. It undoubtedly lasted many hundreds of thousands of years. 

 Much the same conditions prevailed until the titanotheres became ex- 

 tinct. Some of the leaves of the trees are preserved in the beds and 

 some of the logs are petrified. These have not yet been thoroughly 

 studied, but the remains show that the flora has changed much since 

 the Oligocene, and was more like that of the eastern portion of the 

 United States, or of the Mississippi Valley at the present time. The 

 evergreens were represented by the sequoia (related to the redwood of 

 California), and among the deciduous trees are maples, dogwood, 



