218 M. R. Thorpe — John Day Pr ornery cochoeri, 



4,000 feet, while north of the mountains in the fossil 

 localities, Merriam^ considers that the John Day does not 

 exceed a thickness of much over 2,000 feet. 



The John Day formation is divided into three levels, 

 designated as lower, middle, and upper. Paleontologi- 

 cally, the lower has no designation, but the middle is 

 termed the Dice rath erium zone (Wortman), and the 

 upper the Pr ornery cochoer us zone (formerly Meryco- 

 choeriis). The writer considers the designation of the 

 middle zone a misnomer. 



Lower John Day. — This division of the John Day is 

 practically barren of fossils. It lies unconformably^ 

 upon the Upper Eocene Clarno formation, and consists 

 of red, white, and green tufaceous shales. Collier,*^ 

 how^ever, says it overlies the Clarno ''with apparent 

 conformity.'^ This division is between 200 and 300 feet 

 thick and the shale is soft and easily eroded. The char- 

 acteristic erosion topography consists of low rounded 

 mud-covered domes. Collier^ considers these beds of 

 possible Eocene age, to be regarded as part of the Clarno. 



Middle John Day. — This division is characterized by 

 drab and bluish green andesitic tuffs, ranging in thickness 

 from 500 feet at Turtle Cove to 1,000 feet at Bridge 

 Creek. Thin rhyolitic flows are interbedded in the strata. 

 Erosion sometimes produces rounded hills, but more 

 often steep pinnacles and cliffs. Layers of nodules are 

 common and characteristic, in contrast to both the lower 

 and upper divisions. This middle division has furnished 

 the greater number of fossils. The structure shows 

 some tilting and deformation of the strata but not to as 

 great a degree as the lower division. 



Upper John Day. — The upper John Day, 300 to 400 

 feet thick, is composed chiefly of buff colored tuffs or ash 

 deposits, often overlain by sand and gravels at the top. 

 Erosion produces steep cliffs and bluffs. 



At Brid.o^e Creek and Turtle Cove the whole section of 

 the John Day is exposed, while at Clarno the lower and 

 middle beds are well shown. Along Haystack Valley, 

 chiefly upper, but some middle strata are exposed. The 



* J. C. Merriam, IJniv. Calif., Bull. Dept. Geology, vol. 2, 293, 1901. 



^ J. C. Merriam and W. J, Sinclair, Univ. Calif., Bull. Dept. Geology, vol. 

 5, 173, 1907. 



"A. J. Collier, Min. Res. of Oregon, Oregon Bur. Mines and Geology, 1, 

 13, 1914. 



^ Op. cit., p. 14. 



