220 The American Naturalist [March, 



R. E. C. Stearns as F j Lea, is exceedingly 



abundant on stones in the same springs. 



It is a common feature of the Snake Plains, as of many 

 other arid parts of the West, that the rivers which do not sink 

 cut for themselves deep channels with precipitous walls, their 

 present beds being several hundred feet below the general 

 surface level. Of this character are the grand lava canons of 

 Snake River itself and many of its tributaries, particularly on 

 the south side. As a rule these canons cannot be seen until 

 their very brinks are reached, and it is not often that they can 

 be crossed on horse-back. 



The northern boundary of the Snake Plains is formed by 

 the lofty mountains of central Idaho, and by that part of the 

 main range of the Rocky Mountains which bends directly west- 

 ward from the Yellowstone National Park. Three narrow 

 parallel valleys penetrate the mountains of east-central Idaho 

 in a northwesterly direction, carrying slender tongues of the 

 sage plains all the way to Salmon River. 



The soil of the Snake Plains, where not lava or sand, is 

 generally alkaline, and the characteristic plants, in addition to 

 the ever present sage (Artemisia tridcntata), are such Sonoran 

 species as Atriplex crmfertifolia, Atriplex nnitallii, ArUmimtpedrt 

 tifida, Sarcobatus vermiculatus, Tetradymia canescens, Eurotia 

 lo until, Eriogonum cernuum tenue, several species of Bigeloiia, a 

 Malvastrum, and two or three kinds of cactus. Artemisia trljida 

 and Purshia Iridentata are common in the higher levels ; and 

 Iva axillaris, a saline species, was found at the sinks of Big 

 Lost River. 



The characteristic birds of the sage plains are sage sparrow 

 (Amphi«piza belli nevadensis), Brewer's sparrow (Spizella breiverii), 

 sage thrasher (Oroscoptes montanw), burrowing owl (Speotyto 

 cunicularia hypogoea), sage hen (Centrocercus urophasianus), 

 and sharp-tailed grouse (Pediocsdes phasianellus columbianus), 

 though the latter is rare in the area traversed. Ravens (Corvus 

 corax sinuatus) and magpies (Pica pica hudsonica) are common 

 in places, and the canon wren (Catherpes conspersus) was 

 found near Shoshone Falls in the lava cation of Snake River. 



