284 B. N. A. BOUNDARY COMMISSION. 

the nature of the western territories south of the Line, have passed 
through so many phases, that it is important to know that there is a 
a practical limit to the tide of settlement in that direction. Since it has 
been discovered that a great part of this region is not of the nature of the 
typical desert, as had been supposed, there has been a tendency, aided by 
the statements of interested railway and other companies, to elevate it to 
the imaginary position of an agricultural country. Now, however, that 
the crucial test of experience is being applied, and systematic meteoro- 
logical observations are being obtained, it becomes evident that if’ settle- 
ment for agricultural purposes is to pass the 99th meridian, it must do so 
slowly, and strengthening its advance by irrigation and arboriculture. 
The great area based on Cretaceous No. 4, would appear to be absolutely 
irreclaimable. 
657. In estimating the least necessary amount of rainfall for the sup- 
port of cereals, so many circumstances occur to complicate the subject, 
that it is often difficult to arrive at any very exact conclusion. Chief 
among these is the distribution of precipitation with regard to various 
seasons. In ordinary circumstances, only that rain which falls during 
the spring and summer, when the Crops are in the ground, is of import- 
ance. Much, however, depends on the nature of the subsoil, for, where a 
considerable thickness of porous material is based on impervious rocks or 
clays, with a nearly horizontal, or slightly basin-shaped surface, a part of 
the autumnal and winter precipitation, and especially the flood-water of 
the melting snow in spring, may also be countedon. Many considerable 
areas of prairie country are thus situated. The general water level has 
in some cases been ascertained to be not far from the surface, even in the 
autumn, and the moisture rising by capillary attraction prevents the 
entire desiccation of the surface soil. The nature of the soil here enters 
as an important factor. 
658. It is stated by Boussingault, however, that in Egypt, where no 
rain falls during the period of growth, that the distribution of seventeen 
and one-third inches of water over the surface, during the season, of one 
hundred and fifty days, suffices to bring the crops to maturity. The 
ground is here water-soaked to begin with. In India, in a season, of the 
same length, sixteen and one-third inches of irrigation water are dis- 
tributed, the rainfall making the amount up to ‘nineteen and. one-half 
inches. The evaporative effect of the air of the western plains is no 
doubt usually less than that in the countries above named, rendering a 
somewhat smaller quantity of water necessary. 
