206 The American Naturalist. [March, 
the Bad Lands of S. Dakota, which has been more thoroughly 
explored for vertebrate fossils than any other locality in these 
beds. It is located in that portion of Washington county 
embraced between the White and Cheyenne rivers, at that 
point where they approach nearest to each other. This par- 
ticular region has not only proved especially rich in vertebrate 
fossils, but the Titanotherium beds and the entire Miocene 
series, up to the Loup Fork, has attained a development here 
unsurpassed, if not unequaled, elsewhere. In no other region 
has erosion done more to aid the investigator than here; 
whether his aim be to study the country from a purely geo- 
logical standpoint, to collect material for the paleontological 
laboratory, or to study the laws and observe the rate and 
effects of erosion, under the many and varied circumstances 
which this region presents. Since the materials composing 
the Titanotherium beds are very similar throughout the entire 
distribution of the beds, a description of the deposits at the 
typical locality may be considered as representing fairly well 
the character of the deposits at any other locality. 
The section published by Hayden in 1863 agrees in all 
important points with those published since by other authori- 
ties. As stated by Hayden, the beds vary in thickness at 
different localities. At no locality has he given a thickness of 
more than 100 feet. The writer has found, by actual meas- — 
urement, that they attain a thickness in some places at least, 
of 180 feet. As stated before, they are composed of clays, 
sandstones, and conglomerates. The clays greatly predomi- — 
nate, consist of very fine particles, and are quite compact. | Ine 
places they are composed almost entirely of pure kaolin, but 
they often contain a considerable portion of sand. Near the 
bottom of the beds the color is often red or variegated, due to 
the presence in them of small quantities of red oxide of iron; — 
but the prevailing color is a very characteristic and delicate 
greenish white. The clays usually contain little or no cement- 
ing substance, and are held together almost entirely by adhe- 
sion. Occasionally, however, there are quite persistent layat 
of clay nodules, or concretions in which the clays are firmly 
cemented by carbonate of lime. Owing to the extreme min 
