180 



plates, includiug (liagrammatic profiles of Sau Francisco Mountain^. 

 O'Leary Peak aud a volcauic cone north of San Francisco Mountain ; 

 figures representing teeth, skulls, jaws, etc., of various species of animals^ 

 described in the bulletin ; and a map of the United States showing the 

 localities from which specimens of Crotaphytus baileyi and C. collaris 

 have been examined. 



San Fraucisco Mountain was chosen because of its southern position, isolation, 

 great altitude, and proximity to an arid desert. The area carefully surveyed comprises 

 about 13,000 square kilometers (5,000 square miles), aud enough additional territory 

 was roughly examined to make in all about :iO,000 square kilometers (nearly 12,000 

 square miles), of which a biological ujap has been prepared. No less thau twenty 

 new species aud sub-species of mammals were discovered, together with many new 

 reptiles and plants; ajid the study of the fauna and flora as a whole, led to unex- 

 pected generalizations concerning the relationships of the life areas of North America, 

 necessitating a radical change in the primary and secondary divisions recognized. 



The most important part of the general results are: 



(1) The discovery that there are but two primary life areas in North America, a 

 northern (boreal) and a southern (subrtropical), both extending completely across 

 the continent and sending off long interpenetrating arms. 



(2) The consequent abandonment of the three life areas commonly accepted by 

 naturalists, namely: the eastern, central, and western provinces. 



(3) The recognition of seven minor life zones in the San Francisco Mountain re- 

 gion, four of boreal origin, and three of sub-tropical or mixed origin. 



(4) The correlation of the four boreal zones with corresponding zones in the north 

 ;>nd east. 



The relation of a biological survey to agriculture is explained as 

 follows : 



The primary object of mapping the geographic distribution of species is to ascer- 

 tain the number, positions, and boundaries of the natural faunal and floral areas — 

 areas which are fitted by nature for the existence of certain native animals aud 

 plants, and which consequently are adapted for the growth of certain agricultural 

 products and for the support of certain kinds or breeds of stock. The obvious reason 

 why certain animals and plants inhabit restricted parts of the earth's surface and do 

 not occur iu other parts, where there are no impassable barriers to prevent, is that 

 such species have become adapted lo the particular physical and climatic conditions 

 there prevailing, aud their sensitive organizations are not sul3[iciently plastic to en- 

 able them to live under other conditions. 



The present biological survey of the San Fraucisco Mountain region has demon- 

 strated that mammals, birds, reptiles, insects, and plants so coincide in distribution 

 that a map showing the boundaries of an area inhabited by an association of species 

 in one group serves equally well for other groups. The reason of this coiucidence 

 in distribution is that all terrestrial forms of life inhabiting the same area are ex- 

 posed to the same surroundings and governed by the same general laws. 



The point of greatest significance, so far as the practical agriculturist is concerned, 

 is that what is true of animals and plants in a state of nature is true also of animals 

 and plants as modified by the voluntary acts of man; for every race or breed of 

 sheep, cattle, or swine, and every variety of grain or vegetable, thrives best under 

 particular conditions of temperature, moisture, exposure, and so on. It follows that 

 a map of the natural life areas of a country will tell the farmer what he can expect 

 to produce most profitably on his own farm, and also what crops will not thrive iu 

 his neighborhood, thus saving the time and cost of experimental farming, which, in 

 the aggregate, amounts to huudreds of thousands of dollars every year. 



