Forest physiography; physiography of the United States and principles of soils in relation to forestry . ¢ Idem. 44 FOREST PHYSIOGRAPHY Wash., which have such an extremely porous soil of coarse gravel, withonly a thin veneer of silt, that they constitute a locally semi-arid districtin what is otherwise a humid region. The rainfall is about 44 inchesper year, but percolation is so rapid in the loose stony ground thatthe district is a barren island surrounded by dense forests character-istic of the region. Instead of the Douglas spruce {Pseudotsuga taxifolia),the white fir (Abies grandis), the t
Forest physiography; physiography of the United States and principles of soils in relation to forestry . ¢ Idem. 44 FOREST PHYSIOGRAPHY Wash., which have such an extremely porous soil of coarse gravel, withonly a thin veneer of silt, that they constitute a locally semi-arid districtin what is otherwise a humid region. The rainfall is about 44 inchesper year, but percolation is so rapid in the loose stony ground thatthe district is a barren island surrounded by dense forests character-istic of the region. Instead of the Douglas spruce {Pseudotsuga taxifolia),the white fir (Abies grandis), the tideland spruce {Picea sitchensis), andthe western hemlock {Tsuga mertensiana), the district bears the yellowpine {Pinus ponder0so) \ and species of gophers and the desert hornedlark, which are at home in the dry districts east of the Cascades, are alsoat home in this restricted and peculiar area.^ The Coalinga district of California exhibits a plant distributionintimately related to water conditions. Certain gravelly and sandybeds of the district have superior absorptive capacity, while the adjacent. Fig. 5. âIdeal section representing the ground water in relation to the surface and the bed rock. (Slich- ter, U. S. Geo]. Surv.) clay beds have but little power of absorption.^ The sudden rains runoff the clay beds without wetting them notably. The coarse beds aretherefore marked by a varying abundance of vegetation; the clay bedsdo not support vegetation at all. The result is a marked parallelismand alternation of belts of vegetation and belts of barren country insympathy with the belted outcrop of the strata. Forms of Occurrence Water is contained in the soil in three different ways â as groundwater, as capillary water, and as hygroscopic water. GROUND WATER Ground water is the name applied to the water in the saturated zoneof soil or rock; it occurs from a few feet to a few hundred feet below thesurface. Fig. 5; in humid regions it is found usually from five to fifty feet ^
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforestsandforestry
