The effect of this oscillation of the belt of storms, combined with the rise of temperature from winter to summer, is to carry the belt of rainfall progressively farther north during the spring and summer, so that in Texas much of the rain falls in the spring, in Kansas in the late spring and in the Dakotas and Montana in May, June and July. This follows as a natural consequence from the law that precipitation does not take place until the air is cooled below the dew point, and obviously such a cooling would occur much further to the north in summer than in winter.

The Rocky Mountains on the west and southwest of this area form a barrier that intercepts and condenses on its western slopes a large part of the moisture of the air that has succeeded in passing the coast ranges still further west. For this reason the region is semiarid. Thus limited on the west the supply of moisture must come largely from the Gulf of Mexico.

While the rainfall comes mostly in the summer season, due to the conditions stated, the minor amount of precipitation during the rest of the year also comes, in part though less directly, from the gulf, and in part from the evaporation and precipitation of the waters from the adjacent land areas. There is much of this drifting of the moisture of the air, and it has been shown that the rain which falls in Montana, for example, may have been reevaporated and reprecipitated several times on its way from the gulf to the interior.

Snow. The common practice of winter grazing over much of this area indicates that the snowfall is generally light. In favorable years stock feeds out on the plains all winter. The amount of snowfall varies from a few inches to two feet. It usually covers the ground for four or five months, or from sixtyfive to 160 days and little falls before the first of January. Some snow may fall by the first of October, but this usually passes away quickly and a mild period, called "Indian summer" occurs between October and January. Mr. Pease stated the following as examples of winter condition which he observed during a seven years' residence in the area. "In the winter of 1898-99 there was no snow after the October fall, which soon disappeared, until the second week of January; the weather was mild during this time. In 1899-1900 the spring thaw occurred the first week in March, so that plowing was done and seeding over before the first of April. In 1902-03 there was little snow in the vicinity

of Dickinson before the first of March. In 1899 a three days' blizzard occurred the 4th of May, bringing much snow and causing a great loss of stock. The temperature during this storm was not lower than 22 degrees F."

A comparison with the snowfall of the other parts of the United States shows that the Missouri valley has less snow than areas either east or west of it. In northern Michigan, the snowfall is 130 inches; in St. Louis, twenty inches; in Utah and Montana fifty inches; while the average in the Missouri valley is about thirty inches.

The number of days with precipitation, both rain and snow, is about 100. The greatest number of consecutive days with precipitation is from ten to twenty; the greatest number without precipitation varies from thirty to sixty.

Sunshine and Relative Humidity.-Not the least among the elements of climate are those that add to the pleasure of living within an area. Some of the earliest and highest civilizations grew up within regions characterized by a high percentage of sunshine and low relative humidity, accompanied by aridity and rather high temperatures. Especially is it true that the more arid parts of North America were inhabited long before the appearance of the European, by tribes of Indians whose strength of body and vigor of intellect were surpassed nowhere else in prehistoric America.

Just what the beneficial influence of sunshine on the health of man may be it is difficult to state; but it is generally recognized that those lands with a high per cent of clear, sunny days conduce in some way to a more vigorous expression of the vital forces. It is certain that the combination of the sunshine with low relative humidity has the physiological effect of enlivening and stimulating to activity. According to Pettenkofer and Voit,* an adult man eliminates about 900 grams of water from his skin and lungs.daily. Of this amount 450 grams come from his skin alone. A change of even one per cent in the relative humidity of the air causes very perceptible changes in the amount of evaporation from the skin. If the evaporation from the skin is diminished, the amount of urine is increased, and also in many cases the secretions of the intestines, both of which may lead to injurious effects upon the body. Further, the less diluted blood of dry climates acts as a stimulant upon the nervous system, in

*Hann. Handbook of Climatology.

creasing its functions. If not carried to extremes, it will be seen that this latter effect of increasing the nervous activity would be conducive to the higher mental activity, and hence increased culture. It is when dry climates and extremely moist climates are compared that the beneficial effects are most noticeable. Damp air and increased pressure have the following physiological effect: Nervous depression; quiet sleep; increased elimination of carbon dioxide; slower circulation of the blood. Dry air and decreased pressure have these effects: Nervous excitement; sleeplessness; quickened pulse; a drier skin and decreased temperature.

Here it may be stated that the ordinary changes of the atmospheric pressure, equivalent at most to a change of altitude of a few hundred feet, have very little if any physiological effect. The effect is due then, in the cases mentioned above, to the change in the moisture in the air. When the moisture content of the atmosphere is large, the effect of changes of temperature is much more noticeable than when the air is dry. For this reason the inhabitants of deserts and dry climates endure, without discomfort, great changes in temperature which would be intolerable in moist climates. Von Middendorff* in describing the climate of eastern Siberia, says; "It would be impossible for man, with his nomadic habits of life there, to endure the extreme cold of western Siberia unless he were helped by the dryness of the air. Fur clothing which has become damp during the day through evaporation from the body, is laid inside out on the snow during the night and in the morning it is completely dry."

While we do not forget that to the dryness of the atmosphere of this area can be attributed the absence of forests and vegetative productivity which is the source of wealth in more humid climates, yet to the few who live here the extremes of both winter and summer, as well as the greater variability of temperature, are made much more tolerable.

Records show that from forty to sixty per cent of the midwinter and from sixty-five to seventy per cent of the midsummer days are clear. The degree of sunshine increases toward the last of the summer. It may also be said that the density of the cloud bank on cloudy days cannot be as great as that of

*Quoted by Hann from Thomas: Beitrage zur Allgem. Klimatologie.

Place

more humid areas. The clouds will therefore have less effect upon the radiations from the surface of the earth.

The relative humidity, upon which cloudiness depends, is on the average seventy per cent. This is the same as that of Chicago during the dryest days, or when the winds are from the west or southwest.

The following table presents a comparison of the relative humidity of several different areas:

TABLE OF RELATIVE HUMIDITY

The figures of this table show that this region of North Dakota can scarcely be classed with the extremely arid regions of the southwestern and western United States. Rather, it is intermediate between the humid east, and the dry west, and the term sub-humid properly applies to it.

VEGETATION IN THE REGION

Any extended discussion of agriculture and crops is entirely outside the province of this report; as a supplement to what has already been said of climate and irrigation, however, attention will be called briefly to the geographic factors in the distribution of some of the more important agricultural resources.

Some interesting facts concerning North Dakota have been brought out by Mr. Mark Alfred Carlton in a study which he has made of the climate and agricultural products of Russia.*

Mr. Carlton states that many of our most valued varieties of grain came originally from some part of Russia. The red winter wheat called Turkey wheat, which has been grown in the

*Bulletin No. 23, U. S. Department of Agricultue.

great plains for twenty-five years, came from Crimea. Probably, also, the entire group of Fife wheats came from Russia, for they are similar to the Ghirkas of the Volga region. Furthermore, a series of field experiments with 1,000 varieties of wheat, and 300 of oats, barley, rye and spelt, have been carried on by the agricultural department for four years, and it is found that Russian cereals, especially the wheats, are best adapted to culture on the prairie and northern parts of the United States.

The investigations with respect to soils and climate show a striking parallelism between certain parts of central Russia and western North Dakota. First in respect to soils; there is the same gradation between black, humus prairie soil, through acid, neutral and alkaline soils that appears in the prairie of the west; there is also a similar combination in the soil of salts which are useful for plant growth. It is quite likely, although no test has been made, that the soils of the river valleys have chemical and physical characteristics that would make them compare favorably with the "black earth" region of Russia.

The climatic parallel is even more striking. In the greater portion of the two regions the winters are long and severe, while the summers, though short, are intensely hot. Other noteworthy features of the climate are, (1) the great number of clear days in the year, (2) the extreme amount of precipitation during two or three months of summer as compared with that of the remainder of the year, (3) the character of this precipitation, falling in quick thunderstorms, as a rule, with very few days of mist or fog, (4) the excessive heat of midsummer, following intensely cold winters, as already mentioned, and (5) the comparatively light snowfall." These characteristics of climate seem to be more pronounced in Russia than in the area under consideration. It is for this reason that Russian crops seem even better adapted to these northern, semiarid parts of the United States, than to their native habitat.

At Samara, near the heart of the Volga country, the rainfall is 15.6 inches, which, it will be seen is about the same as that of the Little Missouri basin. The normal temperature of Samara, 39.3 degrees F., is slightly less than that of Bismarck, while the July normal is 1.1 degrees higher than at the same place. Botanical investigations have shown that plants subject to the above mentioned characteristics of climate are constituted differently than plants of the humid region. Such plants have

Geology--6