'^^■^ Recent Literature, 



379 



The Boreal Region, as defined by Dr. Merriam, "extends obliquelv across 

 the entire continent from New England and Newfoundland to Alaska 

 and British Columbia, and from about latitude 45*^ north to the Polar 

 Sea," the southern border, however, receding northward "to about lati- 

 tude 54° on the plains of the Saskatchewan." It extends southward in three 

 long arms down the"three great mountain systems of the United States — an 

 eastern arm in the AUeghanies, a central arm in the Rocky Mountains, 

 and a western arm in the Cascades and Sierra Nevada." This latter bifur- 

 cates, "the main fork following the lofty Cascade and Sierra ranges to 

 about latitude 36°, the other following the coast, gradually losing its dis- 

 tinctive characters .... until it disappears a little north of San Fran- 

 cisco" (pp. 22, 23). It is divided into (i) an Arctic division, and (2) a 

 Boreal Coniferous Forest division (p. 24). The Arctic division corres- 

 ponds to the 'Arctic Realm,' 'Arctic Region,' 'Arctic Province,' etc., of 

 nearly 30 previous writers on the subject, of whom about three fourths 

 have accorded it a rank of the first class, and about one fourth as a region 

 of the second class or grade, as is done by Dr. Merriam. The Boreal 

 Coniferous Forest division is about equivalent to the Hudsonian and 

 Canadian faunas (of most recent writers) combined, with their extension 

 westward to the Pacific coast. These subdivisions are referred to by our 

 author as forming "at least two transcontinental zones," called by him 

 respectively 'Hudsonian Zone' and 'Canadian Zone'; he also savs "a third 

 or Timberline Zone may be differentiated from the Hudsonian proper" 

 (p. 24J. 



The Sonoran Region is described as stretching "across the continent 

 from Atlantic to the Pacific, covering nearly the whole country south 

 of latitude 43° and reaching northward on the Great Plains and Great 

 Basin to about latitude 48°," excepting of course the areas along the three 

 principal mountain systems occupied by the southward extension of the Bo- 

 real Region, as already explained. "To the southward it occupies the great 

 interior basin of Mexico and extends into the tropics along the highlands 

 of the interior," and covers all but the extreme southern part of the penin- 

 sula of Lower California (p. 26). The Sonoran Region is divisible 

 "into two principal transcontinental zones (a) Upper Sonoran, and (/>) 

 Lo-wer Sonoran; and each of these may again be subdivided into arid and 

 humid divisions" (p. 27). The 'humid division' of the Upper Sonoran 

 "comprises the area in the eastern United States comjiionly known as the 

 Carolinian Fauna," and merges into the 'arid division' of the Upper 

 Sonoran near the looth meridian. The arid division spreads over the 

 Great Plains, reaching an altitude of about 4000 feet along the eastern foot 

 of the Rocky Mountains in the latitude of Colorado, and extendincr 

 obliquely northward along the Missouri through North Dakota and into 

 eastern Montana. " Another subdivision of the arid Upper Sonoran 

 occupies the greater part of the Great Basin between the Rockv Moun- 

 tains and the High Sierra, reaching northerly .... to and including the 

 plains of the Columbia and Snake Rivers." There is also another area 



