These fundamental differences in the soils of the two regions are illustrated schematically in the subjoined diagram, which shows on the left the contrast between clay or clay loam soils, in which the depth of the surface soil-sample to be taken is prescribed as nine inches by the rules of the Association of Am. Official Chemists (in the writer’s experience it is more nearly six inches as a rule). Alongside of the Eastern soil thus characterized is placed a typical “adobe” soil from the grounds of the California Experiment station, of which a sample showing uniform blackness to three feet depth was exhibited at the World’s Fair at Chicago in 1893. At the right is a profile of the noted hop soil on the bench lands of the Russian river, Cal., in which the humus-content was determined down to twelve feet, the humus-percentage being .44% at that depth against 1.21% in the surface foot (see chapt. 8, p. 139). In this and similar soils the roots of hops reach down to as much as fourteen feet without much lateral expansion; as shown in plate No. 31 of this chapter. Similar conditions prevail in the sandy uplands, as, _e. g._, in the wheat lands of Stanislaus county, Cal., mentioned above. Taking the clay soils as a fair type for comparison, it would seem that the farmer in the arid region owns from three to four farms, one above another, as compared with the same acreage in the Eastern states. _Subsoils and Deep-plowing in the Arid Region._—Up to the present time this advantage is but little appreciated and acted upon by the farmers of the arid region. They still instinctively cling to the practice taught them by their fathers, and which is still promulgated as the only correct practice, in most books on agriculture. There are of course in the arid as well as in the humid region, cases in which deep plowing is inadvisable; viz, that of marsh or swamp lands, as well as sometimes in very sandy, porous soils, the cultural value of which often depends essentially upon the presence of a somewhat consolidated, and more retentive subsoil, which should not be broken up. But in most soils not of extreme physical character, it is in the arid region not only permissible, but eminently advisable to plow, for preparation, as deeply as circumstances permit, in order to facilitate the penetration of the roots beyond the reach of harm from the summer’s drought; while for the same reason, subsequent cultivation should be to a moderate depth only, for the better conservation of moisture, and the formation of a protective surface mulch (see chapter 13). [Illustration: |TYPE OF EASTERN SOILS| TYPES OF CALIFORNIA SOILS. ---+---------------------+--------------------+----------- Ft.| Upland. | Up land clay-loam. | Beach land. ---+---------------------+--------------------+----------- FIG. 27.—Soil Profiles illustrating differences in Soils of Humid and Arid Region.]