FOREST INFLUENCES. 41 



most cases produced no flow in the streams. There is a 

 lake near Devil's Lake, N. D., where in 1890 the old over- 

 land trail leading west terminated abruptly on one side of 

 the lake and was taken up again in the continuation of its 

 direction on the opposite side. The trail is clear and dis- 

 tinct, showing it to have been of comparatively recent use. 

 It is a reasonable inference that when this trail was in use, 

 this lake was dry. There are places near the shores of 

 Devil's Lake where upright stumps are standing submerged 

 in water. The same phenomenon has been noticed in 

 other places. These are almost certain indications of a 

 time or times when the beds of these lakes, where the 

 stumps are, were out of water or very nearly so for a suffi- 

 cient length of time for the trees to grow. The climate 

 must have been very dry, and the great continental plain, 

 or at least portions of it, must have bordered pretty closely 

 upon a desert, and the ''Great American Desert" may have 

 been a reality. It would seem, then, that the knowledge 

 we are gaining of the unknown past, as well as the records 

 of more recent years, point to the recurrence of great fluctu- 

 ations in the annual rainfall of this section, and it seems 

 probable that such changes follow series of years, and that 

 the recedence of our lakes may be followed by periods of 

 higher water. 



But the influence of the cultivation of the soil on water 

 supplies must be taken into account in this connection, for 

 it is undoubtedly true that man has changed the conditions 

 of the soil sufficiently to greatly influence the run-off. The 

 breaking up of large areas of prairie sod, with its low rate of 

 evaporation, and the planting of such land to agricultural 

 crops with a relatively high rate of evaporation, has resulted 

 in a loss of soil water. Then the cultivated soil takes up 

 more water than the sod-bound prairie slopes, so that it 

 does not have so good an opportunity to collect in lakes 

 and swamps, which often supplied the water of wells. And 



