278 . University of California. [vol. 2. 



into the upper or Merycochoerus beds and the lower or Dicerathe- 

 rium beds. 



GENERAL EEATURES OF THE GEOLOGY. 



The section of the John Day formation, as it is known to the 

 writer, includes at least nine formations, showing the following- 

 sequence: — 



River terraces, with undisturbed Quaternary fossils. 

 Rattlesnake formation. Gravels, ash, tuff, and rhyolitic lava. 

 Mascall formation. Ashes, tuffs, and possibly gravels. 

 Columbia lava. Basaltic flows. 



John Day series. Ashes, tuffs, and rhyolite flows. Sands and 

 gravels near the top. Lower, middle, and upper divisions. 

 Clarno formation. Ashes, tuffs, andesitic and rhyolitic lavas. 

 Chico formation. Sandstones and conglomerates. 

 Knoxville formation. Black shales. 



Pre-Cretaceous sedimentaries, serpentines. Granitic masses of 

 unknown age. 



The Knoxville and Chico are marine formations. It is 

 not improbable that some of the eruptives below the Creta- 

 ceous have been intruded into it, though some of them are 

 pretty certainly older than the Knoxville. From the Clarno forma- 

 tion to the top of the series, excepting a very small portion of the 

 whole thickness, the deposits are made up of eruptive materials. 

 The Clarno, John Day, and Mascall are almost entirely composed 

 of ashes and tuffs. They have generally been considered as being 

 wholly lake deposit, but, as will be shown later, the character and 

 occurrence of the fossil remains which they contain are such as to 

 make it doubtful whether they owe their origin solely to this 

 mode of accumulation. 



The Rattlesnake deposits also contain a large proportion of 

 erupted material, but it is mainly composed of gravels derived 

 from the Columbia lava. 



At the close of a long era of erosion following the Rattlesnake 

 epoch, a series of terraces was formed along the main streams. 

 Undisturbed Quaternary remains give definite evidence regarding 

 the age of these deposits. 



