Note 134 — Chapter XX · SOILS OF THE ARID AND HUMID[125] REGIONS.

Looking at the details of the several states, we find that on the arid side Washington has a relatively low figure for soluble silica, which in the average, however, is overborne by the high figures for California and Montana. The explanation of this fact probably lies in the derivation of the majority of the Washington soils examined, from lake deposits brought down gradually from the humid region at the heads of the Columbia drainage, where sandy beds are very prevalent; while the country rock—the basaltic eruptives—are very basic, and moreover slow to disintegrate. In California and Montana the rocks are infinitely varied, and the general outcome of their weathering is plainly a predominance of complex hydrous silicates in the soils, as compared with humid regions.