1893.] The Titanotherium Beds. 207 
uteness of the particles forming the clays and the absence of 
sufficient cementing material in them, in most places they 
readily yield to the action of water and are quite rapidly 
eroded. The clays of the Titanotherium beds were probably 
derived from two sources, viz., from the Cretaceous clays and 
shales, and from the kaolinization of granitic feldspars. 
The sandstones are never entirely continuous, and never 
more than a few feet thick. They present every degree of 
compactness, from loose beds of sand to the most solid sand- 
stones. They are composed of quartz, feldspar and mica, and 
are evidently of granitic origin. When solidified the cement- 
ing substance is carbonate of lime. 
The conglomerates, like the sandstones, are not constant, are 
of very limited vertical extent, never more than a few feet 
thick. They are usually quite hard, being firmly held 
together by carbonate of lime. A section of the beds taken 
at any point and showing the relative position and thickness 
of the sandstones, clays, and conglomerates is of little value, 
since these vary much at different and quite adjacent locali- 
ties. ‘ ; 
The varying hardness of the different strata of the Titano- 
therium and overlying later Miocene beds, by offering unlike 
degrees of resistance to erosion, have succeeded in producing 
in this particular region an exhibition of characteristic Bad 
Lands scenery, unsurpassed elsewhere in the Miocene. The 
surface of the country in this region is scarred by numerous 
deeply eroded canyons. The intervening ridges are rugged 
and barren, often terminating for miles in sharp, serrated 
crests. The walls of these canyons present a series of terraces 
or projecting ledges from top to bottom, due to different 
degrees of hardness in the different strata. Sometimes these 
ledges are but a few feet wide, or just wide enough to allow a 
person on foot to pass along on them. At other times when 
the harder layers of which they are composed are of greater 
thickness, they may be several hundred feet wide, and their 
surface strewn with the fossil bones of Titanotherium, Elo- 
therium, Hyracodon, Hyzenodon, Oreodon, turtles, ete., washed 
