Allen.] o4 [June 3, 



the Yellowstone again at the mouth of Little Porcupine Creek. 

 Thence down the Yellowstone, and eastward to Fort Abraham Lin- 

 coln, on the Missouri, our course was essentially the same as that 

 pursued on our way out. The route of the Expedition hence lay 

 wholly between the 46th and 47th parallels, sweeping somewhat 

 sinuously from one to the other, and extended from near the 100th 

 meridian to the 109th. 



The whole extent of country traversed is thus, in respect to its 

 fauna, wholly beyond the western boundary of the so-called " Eastern 

 Province " of North America, and is comprised within the excessively 

 arid belt of the western plains. But throughout this wide area, 

 the country, either in respect to its general features or its productions, 

 is by no means everywhere alike. The eastern border receives much 

 more rain than the western, and the vegetation is proportionally more 

 abundant and varied, with, of course, corresponding differences in 

 the fauna. Geologically the region is wholly embraced within what 

 has been termed the Lignite Tertiary Formation, but includes limited 

 outcroppings of the Upper Cretaceous. It hence embraces consider- 

 able areas deeply scored by erosion, forming the well-known " Bad 

 Lands " of the Upper Missouri district. A broad belt of these Bad 

 Lands extends along the Little Missouri, and they occur at intervals 

 all along the Yellowstone and its principal tributaries. They form 

 the favorite haunts of several species of animals and plants not 

 found generally dispersed over the plains. 



From the Missouri Biver westward, nearly to the Little Missouri, 

 the country gives evidence of considerable fertility, being covered 

 with a good growth of grass, which the present year remained quite 

 green till our return in September. Along the streams occur scat- 

 tered clumps of timber, composed chiefly of box-elder, elm and 

 Cottonwood, with here and there groves of oak, the latter being 

 confined chiefly to the coulees, or dry ravines, that extend back 

 from the larger streams. Passing this semi-fertile district we arrive 

 at the Little Missouri belt of Bad Lands, twenty to thirty miles in 

 breadth. Beyond these we again meet with comparatively fertile 

 grassy prairies, which extend to the divide west of Inman's Fork of 

 the Little Missouri, or for a distance of some thirty miles. On reach- 

 ing this divide (that of the Little Missouri and Yellowstone) we find 

 indications of a more arid climate, the vegetation becoming more 

 scanty, the grass shorter and thinner, and cacti and sage brush 

 begin to be for .the first time common, and even at times the pre- 



