THE FLORA OF THE GREEN RIVER GROUP. 



GEOLOGICAL DISTRIBUTION OF THE MEASURES. 



In my preceding Reports I have referred to the Green River Group 

 a Umited number of species of fossil plants obtained from different local- 

 ities mentioned below, and which were formerly considered as pertaining 

 to the same geological stage. Now this group includes four members: 

 the lower, the Wasatch, of which the Green River is an upper member; 

 then, in ascending, the Rridger, the Uinta, and the White River with the 

 Oregon beds. 



The name of the Green River Group was proposed by Dr. F. V. Hay- 

 den on account of the great extent, thickness, and display of strata of this 

 formation along X^reen River in Wyoming. 



The formation as it is seen there is purely of a fresh-water origin 

 and seems to be a continuation of the Eocene Laramie Group, or Lignitic, 

 its strata being conformable to it and the modifications of the compounds 

 being gradual. The lower member of the measures is mostly composed 

 of arenaceous beds, the upper a series of laminated shale, each of these 

 members averaging about one thousand feet in thickness. 



The upper part of the measures merit especially to be considered 

 now, as from it are derived the fossil remains which have been described 

 here as derived from the Green River Group. 



The shale, variegated in color, mostly red and white, and variable in 

 thickness, give to the measures a peculiar banded appearance, especially 

 marked near Green River Station, where I had an opportunity to make 

 some observations on the distribution of the strata. At this place a section 

 of 550 feet from the bed of the river to the high round bluff towering there 

 over the country around shows the multiplicity of the layers and the 

 variety of the compound.^ The upper part of the bluff is a hard ferru- 



'Hayden's "Annual Keport," 1872, p. 336, where the section is given in detail. 



127 



