SAVORY PLATEAU REGIOIs^. 165 



by remnants of the Wyoming conglomerate. The best exposures of the 

 Tertiary beds are found in the open valleys at the heads of Savory and 

 Jack's Creeks, and on the pass between the Archaean body of the Grand 

 Encampment Mountains and the Savory Plateau, A thickness of not less 

 than 1,000 feet of these beds is here exposed, which is made up in the upper 

 portion of a thickness of about 300 feet of a drab, earthy, somewhat porous, 

 limestone, sometimes enclosing small pebbles, underlaid by beds, which 

 grade off insensibly from limy sandstones into coarse gravel beds. In the 

 lower part of blnff-exposures bordering the meadows, at the head of Jack's 

 Creek, was found a seam of greenish, indurated clay, containing streaks of 

 fine, hardened gravel, in which are flakes of brown and white mica, deposited 

 with their broad faces parallel to the lines of stratification. In the same 

 bluff was a peculiar seam, a few inches thick, of dark-green, cherty mate- 

 rial, which also contained a few scattered flakes of mica. To the west of 

 the divide, at the head of Savory Creek, the Tertiary beds can be traced for 

 some distance, and are found to cap the underlying Cretaceous sandstones, 

 which are here almost flat, and show no discrepancy of angle. To the west 

 of Savory Plateau, however, and south of the Little Muddy Creek, is an 

 open valley, whose surface is covered by detrital material and considerable 

 accumulations of sand blown in from the open country to the west, in which 

 no outcrops were found. It was impossible, therefore, to ascertain the 

 strati graphical relation of these Tertiaries with the different groups recog- 

 nized in the Green River Basin ; and no beds, corresponding lithologically 

 to these, are found west of this line. Their angle of dip at the most westerly 

 exposures would carry them apparently over the beds of the Vermillion 

 Creek series, and the large proportion of limestone they contain would ally 

 them with the overlying Green River group. They may, however, repre- 

 sent an entirely later series, and be a local development confined to the 

 region of the North Park and the Platte River; for this reason, as has 

 been already stated, they have been designated by a special color, and 

 assigned provisorily to the Pliocene. They occupy the valley of the 

 North Platte to the south of Jack's Creek, forming long, gentle slopes, 

 extending up from the river to the flanks of the Grand Encampment Mount- 

 ains, which, though so covered by recent Quaternary deposits that only few 



