centre of the State. It is very flat, the land sloping gradually from an altitude of a little over 1000 feet along the summit of the ridge to somewhat less than 600 feet on the shore of Lake Michigan and to somewhat more than 600 feet at the Mississippi, a slope of 400 feet in 100 miles. The transverse arm of the ridge is higher and more abrupt, being sometimes called the Penokee Mountains or Range. It stretches parallel with Lake Superior, about 30 miles south of it, and extends eastward into the northern peninsula of Michigan. Its general elevation is between 1500 and 1600 feet, and the highest point within the State is about 1700 feet above sea level. This ridge falls rapidly northward to an altitude of 600 feet on the shore of Lake Superior. A peculiar diagonal valley runs across the State from southwest to northeast, guiding the course of the lower Wisconsin and Fox River, and occupied in the northeast by Green Bay and Lake Winnebago. It is bounded on the south by a somewhat bold escarpment. Otherwise there are no sharp irregularities in the surface except the cliffs along the river valleys in the southwestern part of the State, and the rounded drumlins, mounds, or morainic peaks and ridges composed of glacial drift, which are scattered over the remaining area.
The drainage systems are of course, determined by the three plateau slopes described above. North of the Penokee Range a number of short streams fall into Lake Superior. Those on the eastern slope, flowing into Lake Michigan, are larger, and include the Menominee, which forms part of the northeastern boundary and flows into Green Bay, the Fox, which drains Lake Winnebago and also enters Green Bay, and the Milwaukee River, which flows directly into Lake Michigan. The western and southern slopes of the State, including the greater part of its area, are drained by tributaries of the Mississippi, of which the principal are the Saint Croix, forming part of the northwestern boundary, the Chippewa, and the Wisconsin, the last being the largest river within the State. Several streams rise in the southern part of the State and flow southward into Illinois, all of them joining the Mississippi. The chief of these are the Rock River and the Des Plaines and Fox rivers, two headstreams of the Illinois. The longitudinal divide is so flat that some of its lakes and swamps send their waters in both directions, west to the Mississippi and east to the Great Lakes; this is especially noticeable at Portage, where the waters of the Wisconsin and Fox rivers unite during the floods. A multitude of lakes are scattered over the northern and eastern parts of the State, but only one, Lake Winnebago (q.v.), is of considerable size.
Climate. Owing to the proximity of the Great Lakes, the climate is more tempered than that of the more western interior States, and the range of temperature is not excessive, though the winters are very cold and prolonged. The mean temperature for January is 12.8° at Bayfield, in the extreme northern part of the State, 15.5° at La Crosse, on the Mississippi, and 19.3° at Milwaukee, on the southeastern lake shore. For July the mean is 67° at Bayfield, 73° at La Crosse, and 69.2° at Milwaukee, showing that the summers are cooler on the lake shore than at corresponding latitudes in the interior. The maximum temperature is generally between 90° and 95°, and seldom exceeds 100°; the average minimum is between 10° and 25° below zero. The average annual precipitation for the State is 31 inches, which is very evenly distributed through the State, being only slightly greater in the east than in the west. The greatest amount falls between July and October. Thunderstorms are frequent in summer, but in winter the air is dry and clear, and the snowfall light.
Soil and Vegetation. With the exception of a rocky area in the Penokee highland and an area of poor sandy soil in the central part of the State, the soils of Wisconsin are of good quality. In the northern and eastern sections they are composed of glacial drift and alluvium, forming a rich sandy or clayey loam, while in the southwest there is a very fertile soil formed by disintegration of Silurian limestone. The southern and western parts of the State belong to the prairie region, but in the north and east there are extensive forest belts, which, however, have been much depleted. The forests are largely coniferous—pine, fir, and hemlock—but there is a considerable admixture of deciduous trees, especially on the southern and eastern outskirts, and the composition of the forests in general resembles that of the northern Appalachian region.
Geology. The whole State is of very ancient formation, the uppermost strata being of Silurian or Devonian age. In the north central portion there is a large area of Archæan granites, gneiss, syenite, and other crystalline rocks belonging chiefly to the Laurentian period. They are bounded on the north by rocks of the Algonkian system, which extend to the shores and under the bottom of Lake Superior. On the south the Archæan rocks disappear under extensive beds of Potsdam sandstone which cover a large area in the central part of the State, and which in turn disappear under the Silurian strata. The latter extend along the entire western shore of Lake Michigan and across the southern boundary into Illinois, with isolated patches along the banks of the Mississippi. The most widely exposed member of the series is the Niagara limestone, whose northern escarpment, a continuation of the Niagara escarpment, forms the southern wall of the diagonal valley occupied by Green Bay and the lower Wisconsin River. The Pleistocene ice sheet extended far beyond the limits of Wisconsin, and covered the greater part of it with a layer of drift, but left a large, isolated driftless area in the southwestern quarter of the State. The most important mineral deposits are lead and iron ores. The former are found, associated with zinc and copper, in the Galena or Trenton limestone in the northwestern part of the State, and the iron ores in the Clinton series in eastern Wisconsin, and in the Archæan and Algonkian regions in the north. Granite, sandstones, and limestones are abundant, and cement rock occurs in the neighborhood of Milwaukee. Diamonds have been found in the glacial drift in various parts of the State.
Mining. Wisconsin is rising in importance as an iron-mining State. In 1901, 738,868 long tons of ore were obtained, making the State seventh in rank. There were 725,496 tons of red hematite and 13,372 tons of brown hematite. The ore is obtained mainly from the Gogebic and
