russell.] RELATION OF SPRINGS TO CLIMATE, ETC. 155 
In humid regions the subsoil is normally saturated below a certain 
depth (the water table) and hillside springs are of common occurrence. 
In such regions, also, water is nearly everywhere obtainable by means 
of wells of small depth. In arid regions the subsoil is, as a rule, not 
saturated, owing not only to downward percolation, but also to the dry- 
ing of the surface and the passage upward of absorbed water, through 
capillary action; and surface wells are not successful and hillside springs 
are practically absent. In both humid and arid regions either canyon 
or cave springs are possible, the control passing to topographic condi- 
tions; that is, the depth to which the rocks are cut by canyons and 
valleys determines whether the water contained in previous strata or 
caverns shall outflow or not. In humid regions the general lowering 
of the surface by denudation keeps pace more or less closely with the 
downcutting of stream channels, and deep canyons do not result, 
except under certain highly special conditions. The valleys, as a rule, 
have flaring sides, and are encumbered with debris which tends to 
mask the presence of springs. Although springs of the type of can- 
yon springs do occur in wet regions, they are not common or charac- 
teristic. In arid regions, however, high above sea level, which are 
crossed by rivers rising in well- watered uplands, deep canyons with 
vertical or nearly vertical walls may be produced, and it is in such 
instances that canyon springs reach their most typical development. 
In a large section of the arid region, namely, the Great Basin, canyon 
springs are absent for the reason that the streams are not permitted 
to excavate deep channels. In the Great Basin the valleys are bei in- 
filled or upgraded, and no removal of material from the basin occurs, 
except in a small way through the agency of wind, and this is probably 
compensated for by the dust brought in in a similar manner. 
Fissure springs are possible when water exists in pervious rocks 
under sufficient pressure to force it to the surface if an opening is pro- 
vided. Such openings are produced by movements in the earth's crust, 
and regions not affected by breaks or faults, although water-charged 
beds ma} T exist beneath them, are without fissure springs. Fortu- 
nately the rocks beneath large portions of the arid region have been 
broken, and the characteristic springs, particularly in the Great Basin, 
are due to this cause. 
The favorable result of a combination of climatic, topographic, and 
geologic conditions is illustrated by the fact that canyon and fissure 
springs are not dependent on the precipitation in the immediate vicinity 
of the localities where they occur, but their waters are conducted 
underground perhaps for hundreds of miles without loss by evapora- 
tion, and may rise in a desert locality and give origin to an oasis. But 
for the fortunate combination of conditions referred to, much of south- 
ern Idaho, in common with nearly all of the arid region west of the 
Rocky Mountains, would be far less suitable for habitation than it 
