
CRETACEOUS AND TERTIARY—BAD LANDS. 103 
reached, and a few miles further on, the trail crosses the junction of the 
Tertiary and Cretaceous, and passes out on a lower level plain based on 
the latter formation. Near this place, an exposure shows several seams 
of lignite, one of which appeared to be of good quality® and considerable 
thickness, though not sufficiently well exposed for measurement. This 
bed turns out from the bank in which it occurs, a copious spring of cold 
water, with a very slight ferruginous taste. The associated beds are 
thick arenaceous clays of purplish-brown colour; soft, and containing 
some selenite in crystals. 
Sections in the Bad Lands South of Wood Mountain. 
250. The most instructive section, however, in the Wood Mountain 
region, lies twenty miles south of the settlement of that name, on the 
forty-ninth parallel near the 425 mile point from Red River; here beds 
undoubtedly belonging to the Lignite Tertiary formation,—which, east 
of this locality, has covered so great an area of country,—are found 
clearly superposed on indubitable Cretaceous rocks. The exposures are 
numerous, and are produced by the streams flowing from the southern 
escarpment of the water-shed plateau, above referred to, which has here 
been gashed by their action into most rugged Bad Lands. 
251. This term has attached to it in the western regions of America, 
a peculiar significance, and is applied to the rugged and desolate country 
formed where the soft, clayey Tertiary formations are undergoing rapid 
waste. Steep irregular hills of clay, on which scarcely a trace of 
vegetation exists, are found, separated by deep, nearly perpendicular- 
sided, and often well nigh impassable vallies; or, when denudation has 
advanced to a further stage—and “especially when some more resisting 
stratum forms a natural base to the clayey beds—an arid flat, paved 
with the washed-down clays, almost as hard as stone when dry, is 
’ produced, and supports irregular cones and buttes of clay, the remnants 
of a former high-level plateau. Denudation in these regions, proceeds 
with extreme rapidity during the short period of each year, in 
which the soil is saturated with water. The term first and typically 
applied to the newer White River Tertiaries of Nebraska, has been 
extended to cover country of similar nature in the Lignite Tertiary 
regions of the Upper Missouri, and other Tertiary areas of the west. 
In the Bad Lands, south of Wood Mountain, the hills assume the form 
of broken plateaus; degenerating gradually into conical peaks, when a 
harder layer of sandstone, or material indurated by the combustion of 
