Fig. 5. Mean annual isotherms of North America. (Combined from Chart 20, United States Weather Bureau, and Weather Map of Dominion Meteorological Service.)

tain, as in the Catskill and Alleghany sections, which are really dissected plateaus. Taken as a whole, this province is too rugged for agriculture and much of its surface is therefore still timber-covered; but the valleys, notably the Saint Lawrence, Connecticut and Shenandoah, are often broad, gently sloping, fertile, and well suited to agriculture, and consequently are the seats of important agricultural industries.

"The Canadian Belt is a worn-down mountain region of ancient rocks, in the main too far north for farming, but bearing a great wealth of forest products in its central and southern parts. In its extreme southern and southwestern part this region is in contact with both the Appalachian and Central Plains areas, and there it is often so low, and its topography so moderately irregular, that it is adapted to agriculture. This province extends into the United States along the shores of Lake Superior in northern Michigan, Wisconsin and Minnesota, where it supplies the iron for which that region has become famous.

"South of the Canadian Belt and west of the Appalachian mountains is the largest and most important of the five provinces, the Central Plains. Low in the Mississippi valley and high (5,000 to 6,000 feet) near the base of the Rocky mountains, this belt extends with remarkably level surface from the Coastal Plains of the Gulf shore far northward into Canada. Only in three or four places, notably the hilly regions of central Texas, the mountains of Indian Territory, the Ozark region of Arkansas and Missouri, and the Black Hills of South Dakota, is the surface broken by distinct uplifts where the older rocks have been upfolded into low mountain areas. Elsewhere the strata are essentially horizontal, the surface remarkably level, and the soil deep and fertile. In the east the strata are of paleozoic age, but

in the Gulf states and near the Rocky mountains the strata are younger, notably of cretaceous and tertiary age. This province is one of the greatest grain-raising regions of the world; but in the West, generally speaking west of the 100th meridian, there is too little rainfall for agriculture without irrigation, and this, therefore, is primarily a range country.

"The geology of the Cordilleran region is very complex, including strata of all ages from archean to recent, in all positions from horizontal to strongly folded and faulted, and at all altitudes from below sea-level to the loftiest mountain peaks. In general, the plateaus are made of strata essentially horizontal, the mountains of highly folded and faulted strata. There is every kind of rock and, consequently, a great variety of soils. Here, however, alone of all the provinces, is found in great abundance volcanic rock with its fertile soil. Hundreds of thousands of square miles of country from Canada to southern Mexico are covered by volcanic outflows, the most extensive areas being in the valley of the Columbia and Snake rivers, famous for its wheat production. Much of this province is too rugged for agriculture; far more is too arid; and for these two reasons vast areas of it can never be utilized for farming. In western Canada and northwestern United States there is abundant rainfall; and throughout the area irrigation is employed in areas of ever-increasing extent.

"All of Canada east of the Rocky mountains, and all of the northeastern United States, from New England to western Montana have been invaded, in a recent geological period, by a great continental glacier, which has profoundly modified the topography in detail and imported soils of glacial origin. This glacial invasion covered all of New England, and the outer margin of the glacier extended westward across New Jersey, northern Pennsylvania, thence westward across southern Ohio, Indiana and Illinois to the Mississippi, thence northwestward approximately along the Missouri to the Rocky mountains. In the glaciated area most of the soils are either directly or indirectly of glacial origin and are very diverse from place to place. In the Cordilleran region, mountain glaciers occupied many of the valleys, and often descended to the mountain base and spread out over the plains or plateaus, notably in northern and western Washington."

The northern limit of agriculture on the eastern side of the continent may be set roughly at the fiftieth parallel. This limit bends rapidly northward midway of the continent, reaching the coast region of Alaska. It is approximately the annual isotherm of about 35 degrees. Fig. 5 exhibits the courses of the isothermal lines across the continent. In the northern part, they descend into the middle of the continent, but follow the general course of the parallels, although rising much higher on the western coast. The interior of this vast northern region is approximately level. Much of it is a region of permanently frozen subsoil and with bodies of water ice-filled for a good part of the year. Farther south the isotherms show the interference of mountain masses. There are sharp southward bends in the Appalachian region, and very complicated deflections in the Cordilleran region. On the west coast, the lines are opposed to the parallels of latitude, their positions being determined by mountain chains and Pacific ocean currents. The Pacific coast, therefore, has its own climates, wholly independent of regions east of the continental divide. The temperature factor in the distribution of crops is not well represented in annual isotherms, however, but rather in the ranges and distribution of temperature. The corn-belt and the cotton-belt, for example, do not follow annual temperature lines. Closely associated with temperature are the sunshine Fig. 6. Mean annual sunshine of Canada and the United percentages. Fig. 6 shows the leading areas. This map, by J. W. van Bebber, "is based on the data collected up to the end of 1895, mainly from Jordan photographic sunshine recorders, or from differential thermometers. The distribution is almost homologous to that in Europe. The sunshine increases toward the south and toward the interior, and the more elevated stations have less than those nearer the sea-level. The maximum sunshine is recorded in the north of Mexico, Arizona, Colorado and New Mexico. The sunniest month is May or June in the South, and July in the North, the reverse of what happens in Europe." The precipitation in North America is greatly complicated by the physical configuration. Fig. 7 illustrates this. In the coast regions the oceans control the rainfall. The area of this dominance on the west coast is narrow, however, owing to the mountain barriers, that condense the moisture of the trade-winds. The great Mississippi valley is dominated by the Gulf of Mexico. The cyclonic

movements sent northward from the Gulf are carried eastward by the prevailing winds; were it not for this dominance, the interior valley would be a desert. Between the region of Pacific dominance and Gulf dominance is an immense stretch of arid and semi-arid country. The chart (Fig. 7) shows that the isohyetal of 20 inches runs from Labrador southwesterly to the mid-continent and then turns abruptly southward to the Rio Grande. Other isohyetals of the eastern part of the continent follow a similar course. There are regions of high precipitation at various places along the Atlantic, the Gulf, and near the Great Lakes. In the western part of the continent, the precipitation-lines are local and complex.

The agricultural adaptabilities of the parts and regions of North America have not yet been the subject of careful scientific investigation. The available information is largely descriptive and statistical. Exact studies of the adaptabilities of soils, climates and regions to types of farming mark an advanced stage of agricultural effectiveness. Beginnings are being made in soil surveys and crop surveys. Persons who wish to inform themselves on the geography of agriculture in North America should consult recent books on physical geography; reports on the agricultural capabilities issued by some of the states; publications of the Bureau of Soils of the United States Department of Agriculture, and other publications of the Department; reports of geological surveys in Canada and the United States. A descriptive account of agricultural regions in both North America and South America may be found in Hunt's recent book, "How to Choose a Farm; with a Discussion of American Lands."