The valley of the Yellowstone indicates a great degree of aridity 

 of climate and soil, but the overflowed portions generally afford an 

 abundance of good grass, interspersed, however, with large areas 

 occupied almost exclusively with luxm-iant growths of either Opuntia 

 missouriensis, grease wood (Obione vulgaris'), or sage brush (Artemi- 

 sia canesrens) . The several terraces of the river are even more 

 barren than the bottom-lands, though occasionally affording fine 

 grass, while the plateaus on either side, but especially to the west- 

 ward, are often nearly destitute of grass, the vegetation consisting 

 mainly of cacti and low depauperate forms of Artemisia, and their 

 few characteristic associates. The divide between the Yellowstone 

 and Musselshell, at the point where we crossed it, is also quite simi- 

 lar, a more barren country than that bordering the Musselshell from 

 the 109th meridian to the Big Bend, or than that between the two 

 Porcupine Creeks, being hard to find anywhere east of the Rocky 

 Mountains. 



From Camp Thome, or the " Yellowstone Crossing," nearly to 

 Tongue River, there is very little timber in the valley of the Yellow- 

 stone, frequently not a single tree occurring for miles. Quite large 

 forests begin to appear a little below the mouth of Tongue River, 

 extending up that tributary as far as can be seen from the bluff 

 opposite its mouth, and almost uninterruptedly along the Yellowstone 

 thence, to Pompey's PiHar, forming an almost continuous belt of 

 varying width. The trees are almost exclusively cottonwood, and 

 are many of them of large size. They sometimes form thick forests, 

 half a mile to a mile in breadth, but more frequently grow in more 

 or less detached belts and clumps, being confined to the old beds of 

 the river or its affluents. In the valley of the Musselshell the cotton- 

 wood belt is almost uninterrupted, and is much wider in proportion 

 to the size of the river than that along the Yellowstone, frequently 

 attaining a width of one-half to three-fourths of a mile. The bluff's 

 on the east side of the Musselshell, as far as the Great Bend, as 

 well as the bluffs on both sides of the Yellowstone above the Porcu- 

 pine Creeks, and much of the region between the Mussellshell and 

 Yellowstone, from the Big Porcupine to Pompey's Pillar, is sparsely 

 covered with pines, which attain the height of thirty to eighty feet, 

 and give the country, when seen at a distance, the appearance of 

 being quite thickly wooded. The distribution of the pines serves to 

 mark the extent of the tertiary sandstones, the pines abruptly disap. 

 pearing with the appearance of the cretaceous clays and marls. 



