222 R. W. Chaney — Flora of Payette Formation. 



a higher relief than occupied by the Mascall and other 

 floras of the Miocene. There is some support for the 

 idea of high relief in the coarser phases of the 

 Payette formation, though these are decidedly incon- 

 spicuous. The bulk of the formation appears to be made 

 up of volcanic ash, which may well have been transported 

 by wind, along with the leaves of the upland oaks. From 

 the nearly uniformly fine character of the Payette sedi- 

 ments, a still-water type of deposition may be postulated. 

 The fact that there are no evidences of stream deposits, — 

 lenticular bodies of gravel and sand, and fossil leaves 

 turned into two or three planes during deposition — sup- 

 ports the idea of an area of high relief in which the 

 streams were eroding rather than depositing. In such 

 a region, accumulation of fine sediments and pyroclastics 

 would be going on most conspicuously in the basins of 

 lakes, into which there would also be blown or washed 

 the leaves of trees growing on the slopes above and on 

 the borders of the water bodies. In some such way the 

 plant-bearing portions of the Payette formation may be 

 thought to have accumulated during the Miocene period, 

 with a climate much like that of northern California and 

 southwestern Oregon today. 



Iowa City, Iowa. 



