894 



HISTORICAL GEOLOGY. 



Oreodon beds of sandstones and clays, often nodulous, about 150', with 100' of overlying 

 clays (Wortman) ; and above these the Protocerus beds, sandy below, but clayey above, 

 150', in all 480' thick (Wortman). 



In the region of these basins the strata, owing to erosion by rills and streams from 

 occasional rains, stand in isolated earthworks or embankments, pyramids and spires, over 

 the great plain, looking like a field of desolate ruins, parched and barren in the dry 

 climate. To this region was first applied the term " Mauvaises Terres," or Bad Lands. 



In Oregon, on John Day and Des Chutes rivers, near 120° W., is another lake-basin, 

 the John Day basin (D, Fig. 1468), hardly 500 square miles in area. The Miohippus beds 

 of Marsh, the upper portion, have afforded remains of Miocene Mammals, apparently of 

 a little later date than the White River beds. Marsh correlates with the Oregon Miohippus 

 beds the Protoceras beds of Wortman, stating that the latter contain the Oregon species 

 Miohippus annectens Marsh ; and he further makes his Ammodon beds of the Miocene on 

 the Atlantic border essentially of the same horizon. 



The Loup Fork Group, of the Upper Miocene, was so named from a river in Central 

 Nebraska. The beds cover for the most part the Nebraska lake region (marked N on the 

 map), and its extension southward to Texas, New Mexico, and Mexico. King gives the 

 thickness in Wyoming as 2000'. To the eastward, on the White River, it is 150'. The 

 Deep Creek beds of Montana, first made known by S. B. Grinnell and E. S. Dana (1876), 

 or the Ticholeptus beds of Cope, are referred by W. B. Scott to the earlier part of the 

 Loup Fork epoch. The basin is situated near Camp Baker, 50 miles east of Helena, along 



1409. 

 "^ a 9/) 







KiCHMOND Infusorial Eakth. — a, Pinnularia peregrina; 6, c, Odontidium pinnulatum ; d, Grammatophora 

 marina ; e, Spongiolithis appendiculata ; /, Melosira sulcata ; g, transverse view, id. ; h, Actinocyclus Ehren- 

 bergii ; i, Coscinodiscus apiculatus ; J, Triceratiuin obtiisnm ; k, Actinoptychus undulatus ; I, Dictyocha 

 crux ; m, Dictyocha ; n, fragment of a segment of Actinoptychus senarius ; o, Navicula ; p, fragment of 

 Coscinodiscus gigas. 



