These prairies are traversed by ridges, which facilitate irrigation, and are underlaid by an impervious subsoil, which facilitates both effective storage and drainage.
Carolina on a loose porous sand, which must be at least a foot deep, and contains usually about 8% of clay; this sand is underlaid by a clay subsoil, and, as Mr Milton Whitney points out in Tobacco Soils (U.S.A. Dept.
The plains, except in the south-east corner, are underlaid by sheets of water-bearing sandstone, which carry a volume of water under such pressure that in the valleys of the James river and the Missouri river and its western tributaries a strong surface flow may be obtained from artesian wells.
The Great Plains.A broad stretch of country underlaid by nearly horizontal strata extends westward from the 97th meridian to the base of the Rocky Mountains, a distance of from 300 to 500 in., and northward from the Mexican, boundary far into Canada.
The prevailing type of soil on the higher lands is a sandy loam, underlaid with clay or clay loam, which stores water and is the typical soil of the basins.
Manitoulin Island and the Saugeen Peninsula are comparatively flat and underlaid by a level bed of Trenton limestone.
Cutch and Kathiawar they are underlaid by Jurassic and Neocomian beds.
West of Cracow the Cretaceous beds are underlaid by Jurassic and Triassic deposits, the general dip being eastward.
The superficial Miocene and Pliocene deposits in the west, above referred to, are underlaid by the White river groups of the Oligocene, whose outcrops of Brule clay and Chadron formation also have been mentioned.
M., or almost one-eighth of the area of the state, is underlaid by the coal measures, which occupy a belt in the Cumberland Plateau from 50 to 70 m.