calkins. i Petrography of the John Pay Basin. 



113 



of the region. The thickness of the formation is several 

 hundred feet. The name "Clarno Formation" was given by 

 Dr. Merriam, from the typical exposures at Clarno's Ferry. 



Lithologically, the Clarno is a volcanic, formation, in which 

 truly detrital matter plays an unimportant part. The lower por- 

 tion of the Clarno is composed in greater part of pyroelastic 

 material, while in the upper half lavas, including several different 

 varieties, are abundant. 



The vents through which the lava burst up through the 

 lower tuff beds are exposed to observation in great numbers in 

 the region between Currant Creek and Burnt Ranch. The 

 chimneys of the ancient volcanoes have been filled with lava that 

 has assumed on cooling a beautiful columnar structure, and 

 these volcanic necks, denuded of the less resistant tuffs, form 

 bold, steep-sided "buttes" that are imposing features of the 

 scenery, as well as of great geological interest. 



The John Day Miocene. — The early Miocene, which overlies 

 the Eocene without marked unconformity, is known as the 

 John Day series and has been noted long as a source of 

 vertebrate fossils. Over a broad area in the east-central part 

 of the basin, it is exposed in magnificent cliff sections, attaining 

 a thickness of about 2000 feet. 



The strata of this formation are formed of regularly bedded 

 rocks, red, blue, yellow, and buff in color, generally weathering 

 into typical "bad-land" forms. They are divided by Dr. Mei*riam 

 on lithological and stratigraphical grounds into three horizons, 

 designated as Upper, Middle and Lower John Day. 



We shall show that the principal material in all three 

 divisions is fine-grained tuff. A few thin flows of lava, insig- 

 nificant in volume, are intercalated with the hiffs in various 

 sections, and water-worn gravels and sands occur near the upper 

 limit of the series. 



The Miocene Basalt * — After the John Day tuffs had accumu- 

 lated to a thickness of 2000 feet or more they were subjected to 

 erosion. The inequalities of surface observed by the writer in 

 Turtle Cove at the contact with the next overlying formation 



* Columbia lava as denned by Merriam. 



