Illinois contains probably more coal than any other State in the Union. It is mined at a small depth below the surface, and crops out upon the banks of most of the streams in the middle of the State. These mines have been very imperfectly worked till within a few years; but it is found, that, as the work goes deeper, the quality of the coal improves, and in some of the later excavations is equal to the best coals of Ohio and Pennsylvania, and will undoubtedly prove a source of immense wealth to the State.
The two northwestern counties of the State form a part of the richest and most extensive lead region in the world. During the year 1855, the product of these mines, shipped from the single port of Galena, was 430,365 pigs of lead, worth $1,732,219.02.
Copper has been found in large quantities in the northern counties, and also in the southern portion of the State. Some of the zinc ores are found in great quantities at the lead mines near Galena, but have not yet been utilized. Silver has been found in St. Clair County, whence Silver Creek has derived its name. It is said that in early times the French sunk a shaft here, from which they obtained large quantities of the metal. Iron is found in many parts of the State, and the ores have been worked to considerable extent.
Among other valuable mineral products may be mentioned porcelain and potter's clay, fire clay, fuller's earth, limestone of many varieties, sandstone, marble, and salt springs.
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Illinois has an average temperature, which, if compared with that of Europe, corresponds to that of Middle Germany; its winters are more severe than those of Copenhagen, and its summers as warm as those of Milan or Palermo. Compared with other States of the Union, Northern Illinois possesses a temperature similar to that of Southern New York, while the temperature of Southern Illinois will not differ much from that of Kentucky or Virginia. By observations of the thermometer during twenty years, in the southern part of the State, on the Mississippi, the mercury, once in that period, fell to-25°, and four times it rose above 100°, Fahrenheit.
The prevailing winds are either western or southeastern. The severest storms are those coming from the west, which traverse the entire space between the Rocky Mountains and the Atlantic coast in forty-eight hours.
There are on an average eighty-nine rainy days in the year; the quantity of rain falling amounts to forty-two inches,—the smallest amount being in January, and the largest in June. The average number of thunder-storms in a year is forty-nine; of clear days, one hundred and thirty-seven; of changeable days, one hundred and eighty-three; and of days without sunshine, forty-five.
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The vegetation of the State forms the connecting link between the Flora of the Northeastern States and that of the Upper Mississippi,—exhibiting, besides the plants common to all the States lying between the Mississippi and the Atlantic Ocean, such as are, properly speaking, natives of the Western prairies, not being found east of the Alleghany Mountains. Immense grassy plains, interlaced with groves, which are found also along the watercourses, cover two-thirds of the entire area of the State in the North, while the southern part is garnished with heavy timber.