146 ON THE GEOLOGY AND NATURAL HISTORY 
some cases they have depopulated whole villages. Range: Milk river and Upper Missouri; 
west to the Rocky mountains, south to Red river, southwest to the Upper Rio Grande. 
ARCTOMYS FLAVIVENTER, Bachman. 
YELLOW-FooTeD Marmor. Baird, General Report on Mammals, 1857, p- 835. 
This animal seems to be very rare, but one specimen having been obtained on the Upper 
Missouri. But two specimens of this species are in the museum of the Smithsonian In- 
stitution. Black hills, Nebraska. 
Castor CANADENSIS, Kuhl. 
AmeERICAN Beaver. Baird, General Report on Mammals, 1857, p. 355. 
The Beaver is one of the most interesting and abundant animals in the West. All the 
little streams from Council bluffs to the mountains are occupied to a greater or less extent 
with the indications of their existence. The Yellowstone river, from mouth to source, as 
well as its tributaries, contain myriads, so that they consume literally acres of the small 
cottonwood trees which skirt the streams. ‘These animals are usually quiet during the 
day, but in the far West, they are not unfrequently seen swimming about in the water 
quite unconcerned. The streams that issue from the Black hills are favorite resorts of 
them, and I have often known them to strip the streams of all the timber which skirted 
their borders. On the Yellowstone I saw a cottonwood tree eighteen inches in diameter 
that had been cut down by them. The tree had lodged; they then took off a length of 
two feet. Mr. Weld, a trader who has Spent many years in the West, informed me that 
he has known the Beaver to cut down trees thirty inches in diameter. On Manuel’s creek, 
below the mouth of the Niobrara, a small stream about ten yards wide, I saw five 
dams within the space of a few miles, one of which produced a fall of four fect. They 
vary somewhat in color, sometimes nearly white. One was caught in the Mussel-shell 
river in the Blackfoot country that was a perfect cream color, with red eyes, an albino; 
another from the Big Horn river spotted on the belly like a fawn, and yellowish brown on 
the back. A tributary of Bear river near Great Salt lake is called Black Beaver creek, 
because all the Beaver taken from it are of jet black color. Their skins bring at the pre- 
sent time from three to five dollars each. Range: Throughout the entire area of North 
America. 
GEOMYS BURSARIUS, Rich. 
PouckED on Pocket Gopuer. Baird, General Report on Mammals, 1857, p. 372. 
Very abundant on the rich bottoms of the Missouri, 
where they are exceedingly trouble- 
some to the farmer. One specimen was obtained near the mouth of Vermilion river, and 
a second was caught 
near our camp fire on the Niobrara. This last-ementioned one was 
