Mkrkiam. I 



John Day Basin. 



Without having accurately measured the John Day section, 

 the writer would not be willing to consider the exposures 

 north of the southern range of mountains as representing a 

 thickness much greater than 2,000 feet. Perhaps it is not more 

 than 1,500 feet thick. At Sheep Rock, near Picture Gorge, the 

 whole section is shown rather sharply tilted, and all but the lower 

 division would be included in the column between the cap rock 

 and the level of the river. At Bridge Creek, also, the section 

 includes the whole of the series. It may reach a thickness some- 

 what over 2,000 feet at that locality. 



Classification on Basis of Litlwlogic and Stratigraphic Characters. 

 — Owing to the importance of determining the vertical range of the 

 fossil forms contained in this series, it has been desirable to find 

 some marks of recognition, besides purely palaeontologic charac- 

 ters, by which the beds of widely-separated sections may be 

 correlated. Though no sharply-defined dividing lines can be drawn 

 inside the series, it is still possible, on the basis of both palaeonto- 

 logic and lithologic characters, to subdivide it into several fairly 

 well-marked divisions. 



Wherever the John Day is well exposed in the central and 

 western portion of the basin, it seems to be divisible into three 

 stages, which have been designated* the Lower, Middle, and Upper 

 John Day. 



The lower division consists usually of highly-colored shale, 

 which breaks down readily, forming characteristic mud-covered 

 domes. These beds are in the main a deep red, with occa- 

 sional alternating strata of buff or white ash. At Bridge Creek 

 alternating beds of red, white, and green, occurring in a group 

 of the typical hills of this division, form a striking feature of 

 the landscape, the colored strata making sharply-defined rings 

 about the hills. At Clarno's Ferry numerous alternations of con- 

 torted and faulted, red and white beds are splendidly exposed in 

 prominent hills at the bottom of the section. 



The beds of this group appear usually to show more deform- 

 ation than those higher up in the series. This may be due in part 



-Science, New Series, Feb., 1900. Vol. XI, p. 219. 



