THE MIOCENE PERIOD. 



269 



small areas (lakes?) in southern and central Montana. Later the 

 area of deposition became more extensive, and sediments were spread 

 widely over the area between South Dakota and Mexico. Though 

 the lacustrine and fluvial phases of the formation have not been com- 

 pletely differentiated, it appears that the latter were probably more 

 extensive than the former. 1 To the north, the Loup Fork beds (prob- 

 ably the equivalents of the Arikaree and Gering of western Nebraska 2 ) 

 are often unconformable on the deformed and eroded White River 



Fig. 447. — Court House and Jail Rocks. Buttes of the Arikaree (Miocene) for- 

 mation of western Nebraska. (Darton, U. S. Geol. Surv.) 



beds, and like the latter have given rise to " bad-land " topography, 

 to striking monuments, buttes, etc. (Figs. 447-449). The Santa Fe 

 (fluvial) marls of New Mexico are correlated with the Loup Fork 

 beds. 3 In Texas, beds of terrestrial sediments are wide-spread in 

 the Llano Estacado region, and have been described under the names 

 Loup Fork and Goodnight, though the Goodnight beds are sometimes 

 regarded as Pliocene. 4 



Terrestrial aggradation was doubtless in progress at many other 

 points in the west, though other considerable formations have not 

 been recognized or not differentiated. 5 



x See Haworth, Univ. Geol. Surv. of Kan., Vol. II, p. 281. 



2 Darton, U. S. Geol. Surv., 19th Ann., Pt. IV, and Camp Clarke and Scott's Bluff, 

 Neb. folios, U. S. Geol. Surv. 



3 Johnson, I). W„, Geology of the Cerillos Hills, N. M., Sch. of Mines Quarterly, 

 Vol. XXIV, p. 313, 1903. Bibliography given. 



4 Scott, Introduction to Geology, p. 518. 



6 The relations of the Miocene are shown (under the name of Neocene) on various 



