222 National Geographic Magazine. 
Moreover, from the first table, showing the average monthly 
precipitation at the Helena station, it will be seen that but 4.48 
inches fall during May 15th to August 15th, inclusive, which is 
the growing season when the crops require moisture. 
The information regarding evaporation is as yet very meagre, 
. but from four stations observed in different parts of the State 
during August, September and October, it appears that the total 
average evaporation for the three months was 18 inches, and 
from the best information obtainable it appears that the total 
annual evaporation is 36 inches, that is to say, the surface of the 
water in a lake or reservoir will be lowered by evaporation 3 feet 
in a year. 
Wuy Montana its an Arip Country. 
It has been stated by Major J. W. Powell, that in a general 
way the line between the humid and arid regions, or the amount 
of precipitation below which irrigation becomes necessary for the 
cultivation of crops, is from 24 to 28 inches per annum. This of 
course depends largely on the distribution of the rainfall, the 
proportion falling during the growing season, the humidity of 
the atmosphere, the character of the soil, ete. 
The average annual precipitation in Montana is 14.92 inches, 
while the total average precipitation during the growing season 
is but 5.23 inches ; from these considerations alone it is evident 
that the State lies wholly in the arid region. 
This statement is further born out by the fact that no native 
farmer will settle a ranch or undertake to raise any kind of crops 
without facilities for irrigating, since experience has taught them 
all, that, though there may occasionally be an exceptionally wet 
season in which they can raise good crops without artificial aid, 
still, the years when crops depending wholly upon rain-fall for 
their moisture would be entirely lost, are so frequent as to render: 
farming without irrigation very hazardous and unprofitable. 
Soin. 
The soil along the stream bottoms at a slight elevation above - 
their beds is usually a heavy, black, clayey loam, and though rich 
and fertile is soon clogged by water, and then in drying, cakes on 
the surface, killing the young plants. On this account the irriga- 
tors seldom water these bottom lands until after the crop has 
acquired a healthy growth, preferring to trust to the early rains 
