82 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
other words, below 6000 feet elevation, as the “subdesert” belt (4500 
to 6000 feet), and the “ Gila” belt (2500 to 4500 feet). (See American 
Naturalist, 1893, p. —.) The zone there called “subdesert,” I consider 
Upper Sonoran. 
Mesilla Valley. —The Mesilla Valley of the Rio Grande is about forty 
miles long from north to south, and has an average width of four or five 
miles. It extends from the vicinity of the town of Dona Ana to within 
a few miles of El Paso, thus reaching into Texas territory in its southern 
extent on the east side of the river. This valley is emphatically claimed 
by Dr. Merriara, according to his maps, to be Lower Sonoran , and un¬ 
scientific people often assert it to be “ semi-tropical.” I am perfectly 
convinced, however, that it is to be considered wholly Upper Sonoran. 
Some few Lowet' Sonoran forms may reach it from below by following 
up the river valley, but they are not numerous enough to give it a de¬ 
cided tinge of that fauna. Date palms can not flourish here, even though 
protected through the winter, as has been proved by some sent by the 
Department of Agriculture to Las Cruces in 1889. Some of these are 
Still alive, having been carefully bound up and protected eveiy win¬ 
ter, but they grow smaller and become stunted rather than larger, 
and left unprotected in the winter would speedily die from frost. At 
least one fall of snow occurs every winter as a rule. Oranges are out of 
the question, as well as all sub-tropical fruits. Cotton will not grow to 
best advantage. On the other hand, grapes (except the raisin grape) 
and peaches attain greatest perfection. Every character points distinctly 
to this region as Upper Sonoran. While Larrea tridentata grows on the 
mesas of this region, and even farther north, its distribution in southern 
New Mexico, as has been hinted, is different from what it is in southern 
California. It can not therefore be taken as a criterion of Californian 
conditions in the New Mexico region. 
Organ Mountains. —In the article in Science , already referred to under 
this head, the belts there called “ Dasylirion or Scrub Oak,” “ Mesquite,” 
“ Tornillo or Cottonwood,” ranging from about 6800 ft. down to 3500 
ft., all belong to the Upper Sonoran. 
Other Localities. —All portions of New Mexico below the Transition are 
Upper Sonoran. The same may be said of the southeastern and north¬ 
eastern corners of Arizona and the east central portion. The latter is, 
however, mostly Transition and Boreal. Thus New Mexico possesses 
within its confines only five life-zones: Arctic, Hudsonian, Canadian 
(the true Boreal), Transition and Upper Sonoran. 
The antelope and prairie dog are more or less characteristic of the 
Upper Sonoran. 
Mexico. —A more or less well defined zone of Upper Sonoran extends 
around and throughout the Sierra Madres below the Transition. It ex- 
