382 ORNITnOLOGY. 



mountain ranges and their apparent absence, from the entire intervening 

 territory. Such was particularly conspicuous regarding Sialia mexicana and 

 Lophophancs inornatus, which, if occurring at all in the Basin proper, were 

 so rare that they were not noticed. An apparent explanation of this 

 exceptional range is the general absence of suitable localities over the greater 

 portion of this vast area ; but the circumstance that the species named wei'e 

 still wanting on the Wahsatch and Uintahs, where the conditions of environ- 

 ment are in every way favorable, would seem to suggest other causes. 

 The partial or entire absence of certain woodland species from the sufficiently 

 extensive forests of the higher interior ranges was indeed a subject of con- 

 tinual speculation, since they were searched for in vain, after leaving the 

 Sierra Nevada, until the Wahsatch or Uintah woodlands were reached, 

 when many of them reappeared, while others ilid not, although they are 

 known to occur in the same latitudes on the main Rocky Mountain ranges. 

 Besides the species named above, we may mention Scops flammeola, Glau- 

 cidiiim gnoma, and Cohimha fasciata, which are common to the two widely- 

 separated districts named, but which have not yet been recorded from any 

 intermediate locality; while other species, found both on the Sierra Nevada 

 and Wahsatch, were found to be either extremely rare or apparently not 

 existing at all on any ranges between. These species are the following: 

 liegulus calendula. Parus montanus, Sitta acideata, S. pygmcea, Certhia ameri- 

 cana, and Sphyrapicus thyroideus. All of these, it may be observed, are of 

 pinicoline habits. 



It seems to us that the most reasonable explanation of the abundance 

 of these birds on the Sierra Nevada and Rocky Mountains, and their rarity 

 in or absence from the intervening region, is to be found in the fact that 

 the two great movnitain systems named ap])roximate closely along the 

 northern and southern borders of the United States, thus allowing short 

 and scarcely interrupted passage from one to the other, without being 

 obliged to cross the wide expanse of desert which intervenes along the line 

 of our route. 



The following tables are intended to show more briefly the changes 

 noticed in the bird-fauna during our transit of the Basin, as well as the 

 niiiin lociil ])eculiarities noted by the way : — 



