404 THE AMERICAN NATURALIST.  [Vov. XXXII, 
erosion, and subsequently disappeared, leaving no trace, direct 
or indirect, of its former existence. 
(4) So large a lake should surely have left strongly marked 
wave-cut terraces on its shores and islands. I have never seen 
or heard of any such (as distinguished from wind-cut terraces), 
although the short-lived glacial lakes gave rise to abundant 
evidence of this sort. P 
(c) There is a general absence of minute stratification in the 
clays. They contain heavy beds or layers of different color or 
hardness, but no fine stratification or horizontal cleavage. The 
Niobrara Cretaceous, composed of equally fine material, not 
very different in composition, shows a marked contrast in this 
respect, fine stratification being universal. 
II. Faunal. — These difficulties are yet more serious. 
(a) There are no plants — tree trunks, stems, or leaves — in 
the clays, although these deposits are well fitted to preserve 
them. The plant remains that I have seen are limited to the 
coarser (fluviatile) beds above. Plant remains have been de- 
scribed from the “ Bad Lands of Dakota,” 1 but I do not know 
their exact occurrence. 
(6) There are no aquatic invertebrates. 
(c) There are no fish. 
(d) There are no aquatic reptiles; but land tortoises? are the 
most abundant fossils found, and lizards and snakes occur in 
considerable variety. The only exceptions to this statement, 
as far as I know, are a crocodile skull a 
Trionyx, found in South Dakota ; but wh 
not, I am uninformed? ` 
(e) Mammals occur in 
nd two specimens of 
ether in the clays or 
great numbers and variety, scattered 
all through the clays. Of over fifty genera only three are prob- 
ably aquatic; most of them are land mammals, some are of 
uncertain habitat. The three aquatic forms are a rhinoceros, 
Metamynodon, confined to a single layer of sandstone in the 
Oreodon beds, and an oreodont, Leptauchenia, and a beaver, 
1 Lesquereux. Cretaceous and Tertiary Flora. 
? Family Chersidz, genera Testudo, Stylemys (? = Testudo), 
von Paläontologie. 
One of the specimens of Trionyx is certainly 
— Zittel, Handbuch 
from the sandstones. 
