Page:Isaiah Bowman - Desert Trails of Atacama (1924).pdf/341

 a wide extent of country, such a study would yield results of first importance both to archeology and to geography, to say nothing of its value to the life of the present population or in the development of the soil and water supply for the greater benefit of future population. Were the times and seasons better known and the value of grassland and woodland really recognized, the life of the region could certainly be better adapted to natural conditions. There is now only a primitive relation of culture on the one hand to geographical conditions on the other. The rainfall and run-off of years of heavy pre- cipitation are allowed to waste themselves in gravelly pied- mont slopes and to work destruction upon the cultivated valley lands. The pastures are overgrazed in one part and untouched in another. The waste that has marked the use of water from colonial times still exists.

It has been argued that certain old maps furnish evidence of past changes of climate, notably in the case of the buried algarrobo forests now exhumed in the Desert of ‘larapaca (see p. 16). Such an argument must be taken with great reserve. There are two principal reasons against it. (1) Contemporary evidence of actual forests and a proved knowledge of their extent have yet to be brought forward—the distributions shown on old maps are altogether conjectural and unsupported. (2) It is the habit of piedmont streams like those that descend to the border of the desert of Tarapacd in northern Chile (whence the evidence has come) to shift their courses from side to side; and thus a growth of algarrobo along a given stream channel may be abandoned and left to wither and disappear when the next flood comes down and opens a new channel far to one side. Rainfall so great as to support a general cover of algar- robo forest clearly implies a flooding of the salt-covered basin floors of the nitrate desert, the dissolving of the salt deposit itself and overflow to the sea at the lowest places along the Coast Range. A larger number of woodland patches might occur if the rainfall were increased in the mountains alone and