Merriam.] 



John Day Basin. 



271 



extinct faunas and floras of this region which will follow this paper. 



The writer is indebted to Mr. F. C. Calkins for all petrograph- 

 ical determinations mentioned in this paper. Mr. Calkins has now 

 in preparation an article on the rocks of the John Day region. 



Mr. V. C. Osmont has contributed some valuable information 

 concerning the geology of the region south of the Blue Mountains. 



To Dr. T. W. Stanton the writer is under obligation for the 

 contribution of a note on the Cretaceous fossils collected at Spanish 

 Gulch. 



Prof. T. H. Knowlton has kindly undertaken the study of the 

 fossil plants obtained by the University expeditions, and furnishes 

 for the paper tentative lists of species with a brief discussion of the 

 affinities of the floras. In a bulletin of the U. S. Geological Sur- 

 vey, which is now in preparation, Professor Knowlton will present 

 a discussion of the John Day floras based on a study of all of the 

 collections which have been obtained from that region. 



GEOGRAPHIC FEATURES. 



The existing John Day basin of north central Oregon is a well- 

 defined area almost completely surrounded by the triangular Blue 

 Mountain Range. The rugged eastern ridges, rising to an eleva- 

 tion of over 6,000 feet, are composed largely of pre-Tertiary forma- 

 tions which have been much disturbed. To the west the ranges 

 are made up principally of Tertiary lavas forming regular and fre- 

 quently flat-topped ridges somewhat lower than those to the east. 



Inside the basin are a number of smaller ridges and plateaus, 

 among which the John Day and its tributaries wind in deep and 

 often narrow canons. The streams have here laid bare magnificent 

 sections of all the basin formations, affording unexcelled opportuni- 

 ties for stratigraphic and palaeontologic studies. 



I The main John Day River leaves the west side of the basin 

 through a gap between the north and south ranges of the Blue 

 Mountains. From this point it flows approximately north to the 

 Columbia. Tracing the river back from the gap, its course is seen 

 to be nearly east, till, at the lower end of Turtle Cove, it is divided 

 into two streams, known as the North Fork and the main river 



