with Descriptions of New Species. 219 



lower division is apparently the most disturbed, while 

 the middle and upper are but slightly folded, faulted, and 

 tilted in different localities. The mode of deposition of 

 the John Day is still an open question, but in general, the 

 sediments were probably laid down chiefly by aeolian, but 

 partly by fluviatile agencies, and not wholly by lacustrine 

 as many writers formerly supposed. Whether the ash 

 was poured out in great volume from neighboring vents or 

 whether it was gradually blown into the atmosphere can 

 not be definitely decided at present. If the former, it 

 must have caused the death of great numbers of indivi- 

 duals, and the fact that many specimens of Eporeodon 

 and Pr ornery coclioerus with milk dentition are represented 

 in the collection may have some bearing on the question, 

 which further studies may help to solve. 



The geology of the North Fork of the John Day River 

 is but little known, although it is one of the critical areas 

 of this basin. Geologically, it is important as showing 

 a divergence from the typical John Day formation as 

 elsewhere exposed, in that it exhibits red beds at or near 

 the top. At all other localities in this area, the red beds 

 are apparently confined to the lower John Day. At least 

 one fossil horizon is dark chocolate in color of matrix. 

 Other geologic peculiarities exist in this locality, which 

 are not pertinent to so brief a discussion as this one. On 

 the whole, these beds are probably mainly upper John 

 Day Avith perhaps some exposures of the middle. Paleon- 

 tologically, the North Fork fauna is different froni that of 

 the rest of the basin. Two of the new species herein 

 described were found in this area. Cope indicated this 

 faunal distinction in 1884, and the material of other 

 groups in the Marsh Collection, in so far as it has been 

 worked up and studied, points to the same conclusion. 

 For the present it will be necessary to forego any positive 

 statements regarding either the age or the geologic 

 sequence of this locality, but it is evident that the geology 

 and fauna are both largely distinct in the North Fork 

 region from those of the rest of the basin. 



Geogeaphic Disteibution of Species. 



The majority of the specimens of Promerycochoerus in 

 the Marsh Collection bear accurate field labels, but there 

 are a few of doubtful locality, although from the matrix, 

 and from the letters of the field men, which state where 



