212 The American Naturalist. [March, 
strata had been laid down upon a sloping bottom they would, 
in their lower members at least, partake of the inclination of 
the bottom of the lake. 
About six miles northeast of the town of Chadron, in Dawes 
county, Nebraska, on a small branch of the west fork of Dry — 
creek, the writer, in 1886, while collecting missing portions of © 
the skeleton of Professor Marsh’s type of Titanotherium (Brontops) 
robustum, discovered by H. C. Clifford in 1875, observed several 
feet above the horizon in which this remarkably complete 
skeleton was found, and certainly not far from the top of the 
Titanotherium beds, positive evidence of a break in sedimen- 
tation at this place at least. This evidence consists in the occut- 
rence at this place of a very dark colored layer of vegetable 
mould about two feet thick, accumulated no doubt during 4 
period of elevation above water level. x 
Owing to the fact that the Titanotherium and Oreodon beds 
of S. Dakota and Nebraska are approximately horizontal, itis 
almost impossible to determine there, just what their strati- 
graphic relations are. Farther west, near the head of Lance 
and Harney creeks, in Wyoming, the Titanotherium beds, at 
least, dip to the southward at a considerable angle. The writer 
has been unable to make any but the most superficial obser- 
vations in this region, which, if carefully examined, would 
doubtless furnish a solution of the actual stratigraphic rela- 
tions of these beds. au 
Professor W. P. Jenney, of the U. S. Geol. Survey, 
reported to the writer an account of the discovery of & sM 
Miocene lake in the Black Hills. As a description of th 
singular and interesting deposit a portion of Professor Je 
letter is quoted. He says: “ About 1879-’80 I was into? 
that fossil bones . . . . had been found in a prospe 
shaft near Lead City. I visited the locality and obtained 
session of three nearly perfect skulls a: These mE 
I sent to Professor Marsh at New Haven, accompanied by 
letter giving a sketch and full description of the occur 
and received a reply stating that they were all bape 
bertsonii (this specific name is from memory but E 
correct). iM 
