canaba, and Manistique, draining into Lake Michigan. The Lower Peninsula is watered by the Manistee, Muskegon, Grand, Kalamazoo, and Saint Joseph, which flow into Lake Michigan; by the Cheboygan, Thunder Bay, Au Sable, and Saginaw, flowing into Lake Huron; and by the Huron and Raisin, flowing into Lake Erie. Most of the rivers are small, and the largest are navigable by river boats only for short distances. The morainal districts are also crowded with lakes and ponds, some tributary to the rivers, draining the valleys, others deep tarns caught between the moraines and possessing no outlet. These lakes and ponds of Michigan are estimated at from 5000 to 15,000 in number. The Kalamazoo River alone has within its basin 175 tributary and 150 non-tributary lakes, and other rivers are similarly supplied. They are valuable sources of water supply, and when they disappear their beds furnish a black muck soil with a shell marl subsoil which is excellent for garden culture. Other lakes owe their origin to the erosion of limestone forming caves and sink holes, or to the sand bars built across the mouths of bays or rivers by the Great Lakes at the present or at a higher stage of elevation. Still another source of these numerous lakes is the tilting of the earth's crust which flooded old river valleys and landlocked the waters within. If Professor Gilbert's theory is true, this process is even now going on. If the land is rising five inches a century per hundred miles along an axis through Niagara Falls and northeastern Michigan, it is easy to see that Saginaw Bay will soon be a lake. In fact, even now it is practically stagnant.
Upward of 200 islands belong to Michigan. The largest are Isle Royale and Grande Isle in Lake Superior; Sugar Island, Encampment Island, Drummond Island, Bois Blanc, Mackinac, and Marquette at the head of Lake Huron; and the Beaver, Fox, and Manitou groups at the head of Lake Michigan. The chief indentations of the coast of the Lower Peninsula are Grand and Little Traverse bays on the northwest, and Thunder and Saginaw bays on the east side. In the northern peninsula are Keweenaw Bay east of Keweenaw Peninsula, and White Fish Bay on the northern shore at the west end of Saint Mary's River. On the south are the Big Bay and the Little Bay of Noquet at the head of Green Bay. One of the interesting features of the Michigan coast is the ‘Pictured Rocks’ on the northern coast of the northern peninsula, where the Cambrian sandstones are carved by the action of the water into fantastic shapes—arches, towers, castles, etc. In some places steamers can pass directly under the rocks and behind falling cascades.
Climate. Though Michigan lies in the heart of the north temperate zone, the northern peninsula has a rigorous climate. Only in the southern tier of counties are the plant and animal species wholly austral. The average track of the extra-tropical cyclonic storms for all the continent crosses the State. Over 450 such disturbances passed that way in ten years. The average temperatures for July are 65° F. for Bessemer and Mackinac, and 70° F. for Detroit. The southwestern side of the Upper Peninsula and the southeastern corner of the Lower Peninsula have a maximum temperature of 100°. The winter minimum is 20° below zero for Detroit, and 30° below at Keweenaw Point. This gives a range of 130° for the Upper Peninsula and of 120° for the Lower. Sault Sainte Marie holds the United States record for the frequency of cold waves, with a fall of 20° F. or over in twenty-four hours. The average rainfall for the State is 30 inches. The northern peninsula from Keweenaw Point to Sault Sainte Marie holds the record in the United States for the heaviest annual snowfall, 130 inches. This is reduced to only 40 inches at Ann Arbor. Presque Isle County has precipitation, on the average, 170 days in the year, sharing with Buffalo the highest record in the United States east of Cape Flattery. The prevailing winds for January and July alike are southwest for the Lower Peninsula and northwest for the Upper. There are on the average twenty thunderstorms per year, with a maximum frequency in July.
For Flora and Fauna, see these sections under United States.
Geology. The State of Michigan in its Upper and Lower peninsulas has all the recognized series of rocks from Archæan to Carboniferous inclusive. The earlier part of this record is represented in great detail in the rocks of the northern peninsula. In fact, the region around Lake Superior, including northern portions of Minnesota, Wisconsin, and Michigan, has had an extremely involved geological history, the careful and detailed study of which, by a host of geologists, has added more largely to our knowledge of pre-Cambrian geology than any equivalent area in the world. This study has disclosed a whole system (Algonkian) of rocks below the Paleozoic, representing perhaps a longer lapse of ages than all the time since the beginning of the Cambrian. The earliest beds of the Algonkian are much metamorphosed and cut in every direction by dikes and sills of igneous intrusives and extrusives. The Penokee-Gogebic and the Marquette-Menominee members of this system are the great iron-bearing beds of the northern peninsula. They dip down under the bed of Lake Superior and outcrop again in the Vermilion and Mesabi ranges in Minnesota. At the top of the Algonkian are the copper-bearing beds. The copper is found usually in elastic beds, largely in conglomerates, though sometimes in sandstone and adjacent lava sheets.
The Lower Peninsula of Michigan is essentially a bowl-shaped depression in the pre-Cambrian crust, between the old Archæan island of North Wisconsin and the similar island of the Adirondacks. This grand synclinal trough was being filled with sediments through Cambrian, Ordovician, Silurian, Devonian, and Carboniferous ages, the successive deposits lying like a pile of saucers, with outcropping edges all dipping toward the centre. In Sub-Carboniferous time the basin was a narrow-mouthed bay, acting as a saltpan, concentrating sea-water and depositing beds of rock salt. In upper Carboniferous some beds of coal were laid down. The State has evidently been continuously above the sea since Carboniferous time. The present surface of the State is largely determined by glacial action, being very much smoothed over, and covered with a sheet of till, in some places some hundreds of feet in thickness. The present rivers are consequent upon the drift surface, and many smaller lakes have a glacial origin.
The soil on the whole is extremely fertile, being made up of the glacial detritus of lime-
