214: R. W. Chaney — Flora of Payette Formation. 



Art. XXL — Notes on the Flora of the Payette For- 

 mation; by Ralph W. Chaney, Carnegie Institution 

 of Washington. 



The Payette flora as described by Knowlton in 1898 1 

 is made up of 32 species. It was referred by him to the 

 Miocene because of its resemblance to the Upper Clarno 

 and Mascall floras of the John Day Basin which were 

 supposed at that time both to be of Miocene age. Later 2 

 the same author determined the age of the Payette as 

 Upper Eocene, because of its resemblance to the Upper 

 Clarno flora which his later "work had shown to be of 

 Upper Eocene age. 



The present paper is based on observations and collec- 

 tions made in southwestern Idaho and adjacent Oregon 

 during the season of 1921 under the auspices of the Car- 

 negie Institution of Washington. Its purpose is to add 

 to the number of forms of fossil plants known from the 

 horizon, to present further evidence regarding their age, 

 and to make suggestions regarding the conditions under 

 which they lived. 



The Payette formation comprises several hundred 

 feet of sediments overlaying a basalt series which 

 appears to be an eastward continuation of the Colombia 

 lavas. According to Buwalda 3 its basal portion is inter- 

 stratified with these lavas on the south side of the 

 Snake river valley. Where studied in connection with 

 its plant fossils, the Payette is made up largely of a 

 fine gray salmon-colored shale, highly indurated. In the 

 vicinity of Montour, Idaho (the Marsh postoffice locality 

 of Knowlton and Lindgren), there are conspicuous white' 

 shales made up of diatomaceous sandy material. Lig- 

 nite seams are of common occurrence, and locally the 

 sediments appear to be made up of broken-down granite. 

 Fossil plants are found most frequently on small slabs 

 of the highly indurated shale which have been weathered 

 loose and scattered over the slopes of the hills. They 

 have been collected by the writer at the following 

 localities : — 



1 Knowlton, F. H. ; Fossil Plants of the Payette Formation, U. S. Geol. 

 Survey, 18th Ann. Kept., Pt. 3, pp. 721-744, 1898. 



2 Knowlton, F. H. : Fossil Flora of the John Day Basin, Ore., U. S. Geol. 

 Survey, Bull. 204, pp. 110-111, 1902. 



3 Buwalda, John P.: Letter of Nov. 6, 1921. 



