174 LOCALITIES OF NATURAL SUPPLY. 



moisture sufficient, it will continue to grow for the whole term of its life, independent of month' 

 and season, converting the annual of the north into biennials and perennials further south. 



It is, therefore, to the sufficient supply of ivafer in the soil that the growth, whether at the 

 outset or in continuance, takes place. The fall of rain does not influence this growth, except 

 in so far as^it saturates the soil. Hence, when we say that a fall of rain does not occur at the 

 time suitable for vegetation, we mean that the rain fall does not sink into the earth — that it is 

 either wholly or mostly evaporated by the excessive temperature. If this be true, the rain fall 

 is not sufficient to supply depots of water for artesian borings. Thus the absence of vegetation 

 is an evidence of a deficient supply of water. 



Now, when irrigation is applied to those plains susceptible of supply from rivers, the thorny 

 vegetation disappears. The obione, the larrea, artemisia, fouquieria, and the pitahaya, all are 

 removed, and the mesquite, the willow, the cotton-wood, and other grasses supply their place ; 

 and so universal is the occurrence that the observing traveller can at once tell what is the 

 hygrometrical condition of the ground, or subsoil, by an examination, at a glance, of the super- 

 ficial growth. 



From frequent observation, when travelling over this route, I have constructed the following 

 table, which gives an approximate estimate of the value of vegetation, as an indication of the 

 moisture of the subsoil : 



1. Subsoil saturated with standing water — Tule or Carrizo, (Arundo phragmites ; A. tessaria.) 



2. Moving water, with pools— ?-Ms/ies, (Juncus ;) willow, (Salix.) 



3. Surface soil moist — Plantago, cotton-wood, (Populus monlifera.) 



4. Six feet above river level — Cedar, (Juniperus ;) dwarf oak, (Quercus ;) walnut, (Juglans ;) 



bunch grass. 



5. Fifteen to 30 feet above river level — Mesquite, (Algarrobia ;) screw lean, (Prosopis ;) tunal, 



(Opuntia.) 



6. Above 50 feet — Maguay, (Agave Americana ;) yucca, Spanish bayonet, (Palmetto ;) gramma 



grass, (Bouteloria.) 



'7. Where the foregoing plants disappear on level plains — Creosote plant, (Larrea Mexicana ;) 

 stink weed, (Eriodyction ;) grease wood, (Obione canescens ;) wild sage, (Artemisia.) 



On elevated granitic soils — Pitahaya, (Cereus.) 



In the most arid soil — St. Joseph's rod, (Fouquieria.) 



Thus it is derived from observation that, by an inspection of the vegetation, we can form an 

 estimate, not of the exact fall of rain, but of the moisture of the soil — that is, of the rain fall, 

 which is available for wells and springs — and thus the conclusion, drawn in the absence of 

 information derived fom the rain guage, is not likely to be far from the truth, or to lead to any 

 great error in practice ; for had sufficient rain fallen over and above evaporation on level plains, 

 it would be elevated by capillary action to supply a new vegetable growth. 



As for the water supplied by melting snows descending from the summits of lofty hills, and 

 sinking between the strata and at the base, along the parallel examined, where there are lofty 

 ranges, as the Organ mountains, Mogollon mountains, and the Pinaleno hills, there are also 

 rivers formed, as the Bio Grande, Gila, and San Pedro ; but as for the smaller chains, as 

 Chiricahui, and others of less note, the quantity of snow collected is much less, and merely 

 waters the cations of the ranges ; and by the time the stream has passed to the edge of the 

 plain, it is dwindled down to an insignificant thread, which is lost by evaporation. 



In thus condemning attempts to obtain water by artesian borings for railroad purposes, I do 



