Page:Popular Science Monthly Volume 80.djvu/216

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Size of Soil Particles[1]

Size in mm. 2.0-1.0 1.0-0.5 0.50-0.25 0.25-0.10 0.10-0.05 0.05-0.01 0.01-0.005 0.005-0.0001
Station 1 0.00 0.12 3.28 70.05 22.29 1.14 0.23 2.12
Station 2 0.00 0.41 8.59 46.62 39.56 0.86 0.28 3.35
Station 3 0.08 1.15 8.20 10.07 39.17 2.98 0.63 5.05
Average of 3 stations 0.02 0.56 6.69 52.24 33.67 1.66 0.38 3.50

Such a loose sandy soil soaks up moisture very readily, so that after a heavy fall of rain scarcely any water is drained from the surface into the valleys, but all of it goes into the porous soil. Now and then rainstorms of such torrential fierceness occur in the hills that a great quantity of the sand is brought down from high on the hills and carried into the valleys. Such storms are, however, exceptional, since the usual heavier rains of about 1.0-1.5 in. are completely taken up by the sand, with no surface drainage at all.

In connection with the distribution of soil water in the Sand Hills it is interesting to note that, although the surface of the sand is commonly as dry as powder, the sand but a few inches beneath the surface is quite moist. The average of many soil samples taken during July, 1911 (a wet month for that year), in widely isolated stations at a depth of twelve inches, showed the water content to be 3.27 per cent. The Sand Hills rest upon a series of relatively impermeable clays and stratified rocks. These layers of more solid materials crop out from the surface along streams and on the lower slopes of some hills quite remote from the deeper valleys. The soil is always moister upon a slope with these outcrops than in situations where such are absent.

The annual precipitation over the main body of Sand Hills varies from twenty-three inches in the east to about fifteen inches on the western border. April, May and June are usually the wettest months of the year, while the dry season frequently continues from August to March or the first of April.[2] In the central Sand Hills during the month of July, 1911, five and one half inches of rain fell. At the government forest nursery near Halsey (Thomas County) during this month there was scarcely a day that rain did not fall. The showers were usually light, but a few were soaking rains. Hail sometimes accompanies these thunderstorms in such quantity that a great amount of damage is done to gardens, crops and other property.

Most of the precipitation disappears into the soil at once. It is a rare sight, if indeed it ever happens, that any of the streams or lakes of the region show an increase in volume resulting from the run-off from

  1. From Professor E. H. Barbour, Nebr. Geol. Survey, Vol. 1, 1903.
  2. Data from official records of U. S. Forest Service at Halsey, Nebr., for last seven years.