The American Geologist. October, 1 •.-,... 
js has been made in the distinction of the geological and 
fauna! zones. Pen years ago the accurate geological ob 
servations of Hayden were overlooked, and ii was believed 
that formations equivalent to the Middle and l own Mio 
cene of Europe were sparser) if al all representetd. X"\\ 
three fauna! are clearly re< d (Scott 1 , Matthew . 
Gidley'), namel) : Lower (Rosebud beds), in which the ani 
mals arje still sparsel) known. Middle (Deep River beds), m 
which the fauna is becoming move full) known. Upper 
(Loup Fork beds), in which a ver) rich (anna is now fully 
known. Each of these divisions is distinguished b) specific 
stages in the evolution of the horses, rhinoceroses, camels. 
oreodonts, rodents, and carnivores These chronological 
successions derived from geology have already yielded verj 
important new biological results. 
The zoogeographical relationships with Europe have 
been strengthened by the discovery for the first time oiDin- 
'» ( Matthew 1 ), of a new Species oi rhinoceros ^ Tele- 
os bicornutus* Osborn), closely similar to the Tdeoceros 
aurelianensis of the Lower Miocene of France, by the rec- 
ognition of new Mustelidae (Lutra), and of the Castoridae 
{Dipoides). The Proboscidea, now known to be of African 
origin, arc not certainly found in the lower and sparsely 
known in the middle. bu1 arc fully represented in the upper 
beds. In the middle beds appears Mastodon productus r 
rather derivable from the Palaeomastodon, of Africa than from 
the J/, angustidens of France. 
Our views as to the Miocene climate have also under- 
gone a change, owing to the recognition that most of these 
deposits are tlnviatile and aeolian rather than lacustrine 
(Matthew. Gidley*), as evidence oi a dry climate, marshy 
• Beds, Trans. Amor. PhilOS S 
\ 805, pp. 55- - 
the TerUary, etc Mem. a M N 11. vol i. 1901, 
•>i the .1.'. . Bull. Amor. 
Mus \. 1904, pp. 241. 
Bull. Amor. .\lus 
\ : Hist., vol xvi. 1902/pp. l^-lSfi. 
Hull. Amor. Mus. Nat. Hist., vol \\ 
1904, pp. S07-S26. 
• s Dakota 
Bull. Amor. Mus Nal Hist., vol. xx. 1904, pp. :M1-lVs 
