170 



University of California. 



[Vol. 3. 



view, we have tabulated here the succession in. the John Day 

 Basin. While in certain details it maybe defective or doubtful, 

 it probably gives the main facts with substantial accuracy. 



j Hornblende -andesite. 



Clarno Eocene \ ^xene-andesite, basic. 



\ (Quartz Basalt. 



( Kliyolite. 



(" Trachyte (?) tuff. 



John Day Miocene -< ^J 1 ^?" 6 tu f ■ , ', . ' ,. „ 



' \ Rhyolite and rhyolite tuft (in small amount). 



[ Andesite tuff. 



Basalt, thickness over 2000 feet. 



f Rhyolite tuff at base. 

 Mascall Miocene < Basalt, interbedded with basal beds. 



( Rhyolite tuffs (probably). 



Rattlesnake Pliocene J Rhyolite and rhyolite tuff. 



The general order seems to afford a fairly strong confirmation 

 of Iddings's theory that the normal succession is from interme- 

 diate to more basic and more acid types. 



In the Eocene we seem to have a complete cycle in accordance 

 with this theory. The period extending from the base of the 

 John Day to the top of the Rattlesnake formation may be 

 considered as a second cycle, though the presence of rhyolite, 

 apparently balanced by no corresponding basic eruption, in the 

 middle of the John Day andesite tuffs, indicates an apparent 

 failure of the rule. Since, however, such a basic member was 

 not especially looked for, a failure to observe it does not prove 

 its absence. 



The recent ash may represent the first term of a third cycle. 



CONDITIONS OP ACCUMULATION OP THP TERTIARY DEPOSITS. 



The supposition that the fossil beds of the John Day region 

 were of lacustrine origin seems to have been generally accepted 

 by early writers, perhaps tacitly and without critical examination. 

 Of late, however, this view has been subjected to criticism, and 'in 

 the writer's opinion shown to be absolutely untenable in connec- 

 tion with the greater part of the deposits in question. 



Dr. Merriam* and W. D. Matthewt have discussed the 



* Op. cit., p. 299. 



t Am. Naturalist, May, 1899, vol. 33, 



