Absence of great variation in physiography gives all portions of the State an almost uniform climate. North Dakota is situated in a temperate region of moderate rainfall, and owing to its position in the center of the North American Interior Plains it has a typically continental climate. One of the characteristics of such a climate is a wide range of temperature, and to this the State can make good claim. North Dakota has a recorded range from 124° F., registered September 3, 1912 at Medora, to -60° F., recorded February 15, 1936 at Parshall. These temperatures are, of course, unusual, but the mercury often reaches 100° F. during the summer, whereas 30° to 40° F. below zero is not uncommon in winter. The mean temperature for the months of June, July, and August is 65.7° F., and for December, January, and February, 9.7° F. Relatively low humidity, averaging 68 percent, makes these extremes less uncomfortable, however, than if the atmosphere contained more moisture. The sections of the State vary more in the matter of precipitation than in any other climatic phase. The average is about 18 inches annually, ranging from about 22 inches in the southeastern corner to about 14 inches in the southwestern corner. Most of the precipitation occurs in the late spring and summer. During the period of 1925-34, three years had a rainfall in excess of normal, and seven were deficient in precipitation. Long and severe winters are typical of this region. Nevertheless the summers, though comparatively short, are favorable for agriculture, owing to the long hours of sunshine. At the maximum, about June 21, there are as many as 16 hours of sunlight a day; and this, together with cloudless skies, contributes to the rapid growth and early maturity of crops. HOW THE LAND WAS FORMED The surface of North Dakota, comparatively unvaried, is no more simple than the geological pattern that lies beneath it. Deposited by the seas of three geologic ages, horizontal layers of rock top each other in methodical and unintricate succession. In far-off Paleozoic times, when all creatures of the earth were invertebrates, strange shellfish, unlike any existing today, lived among the rich foliage at the bottom of the shallow sea that covered this region. Hundreds of varieties of fossil plants and shells are embedded in the sandstone, limestone, and shale which the sea deposited on the uneven surface of the then-existent crystalline rocks. These Paleozoic rocks have been encountered in deep wells in eastern North Dakota, although nowhere in the State are they found at the surface.