IMPORTANT QUESTIONS RELATING TO IRRIGABLE LANDS. 87 
geographical operations. To run hypsometric lines with spirit levels would 
have involved a great amount of labor and been exceedingly expensive, 
and such a method was entirely impracticable with the means at command, 
but the methods used give fairly approximate results, and perhaps all that 
is necessary for the purposes to be subserved. 
THE SELECTION OF IRRIGABLE LANDS. 
From the fact that the area of arable lands greatly exceeds the 
irrigable, or the amount which the waters of the streams will serve, a wide 
choice in the selection of the latter is permitted. The considerations affect- 
ing the choice are diverse, but fall readily into two classes, viz: physical 
conditions and artificial conditions. The mountains and high plateaus are 
the great aqueous condensers; the mountains and high plateaus are also 
the reservoirs that hold the water fed to the streams in the irrigating season, 
for the fountains from which the rivers flow are the snow fields of the 
highlands. After the streams leave the highlands they steadily diminish in 
volume, the loss being due in part to direct evaporation, and in part to 
percolation in the sands from which the waters are eventually evaporated. 
In like manner irrigating canals starting near the mountains and running 
far out into the valleys and plains rapidly diminish in the volume of flowing 
water. Looking to the conservation of water, it is best to select lands as 
high along the streams as possible. But this consideration is directly 
opposed by considerations relating to temperature; the higher the land the 
colder the climate. Where the great majority of streams have their sources, 
agriculture is impossible on account of prevailing summer frosts; the lower 
the altitude the more genial the temperature; the lower the land the greater 
the variety of crops which can be cultivated; and to the extent that the 
variety of crops is multiplied the irrigating season is lengthened, until the 
maximum is reached in low altitudes and low latitudes where two crops 
can be raised annually on the same land. In the selection of lands, as 
governed by these conditions, the higher lands will be avoided on the one 
hand because of the rigor of the climate; if these conditions alone governed, 
no settlement should be made in Utah above 6,500 feet above the level of 
the sea, and in general still lower lands should be used; on the other hand 
