THE MIOCENE PEB10D. 



267 



for this formation. 1 With one exception, the fossil plants of the series 

 are new. 2 In Montana, the Miocene sediments (Bozeman formation, 

 Fig. 446) are described as lacustrine, and are said to have a thick- 

 ness of nearly or quite 2000 feet. They consist of gravel (conglomer- 

 ate), sand, clay, limestone, and volcanic dust. 3 In this region some 



Ellensburg formation, 

 1000-1500 feet 



Yakima basalt, j Kl fflW 



B-3 



1000-2000 feet 



Taneum andesite 



Manatash formation, 

 1000 feet ± 



Easton schist 



H I 



Fig. 445. — Columnar section showing the succession of formations in central 

 Washington. (G. O. Smith, U. S. Geol. Surv.) 



of the cones built up by old hot springs, and subsequently buried by 

 clastic sediments, are still preserved. 



Farther east, on the western part of the Great plains, the depo- 

 sition of the White River beds may have continued for a time after 

 the beginning of the Miocene, as indicated by the fauna of the upper- 

 most beds. Late in the Miocene period, aggradation seems to have 

 been renewed in the same general area, and the Loup Fork formation, 

 thin but extensive, was spread out over the western plains. In the 

 early part of this epoch (sometimes called the Deep River stage) the 

 deposits were of slight extent, being apparently restricted to several 



5 Turner, Am. Geol., Vol. 29, p. 268, and 21st Ann. Rept, U. S. Geol. Surv., Pt. II. 



2 Op. cit., p. 219. 



3 Peale, Three Forks folio, U. S. Geol. Surv. 



