ILLINOIS 183 on the Ohio, constituting the fruit region of southern Illinois. The chief rivers within the state are the Rock, Illinois, and Kaskaskia, affluents of the Mississippi ; the Emharras and Little Wabash, tributaries of the Wabash; and the Saline and Cash, which fall into the Ohio. The Illinois is much the largest of these ; its constituents are the Kankakee from Indiana and the Des Plaines from Wiscon- sin, and in its entire course of nearly 500 m. (245 navigable) to the Mississippi it receives the Fox and Spoon rivers and Crooked creek from the right, and the Vermilion, Mack- inaw, Sangamon, &c., from the left. It has a wide deep bed, and in some parts opens into broad and lake-like expanses. Rock river also rises in Wisconsin, and has a course of 300 m. to the Mississippi; it is imperfectly navigable for 75 m., and its upper course is impeded by rapids. The Kaskaskia has its sources in Champaign co. (in which also rise the Sangamon, Embarras, and the southern constituents of the Vermilion), and pursues a direction nearly parallel with the Illinois; it has a length of 250 m. The Big Muddy, an affluent of the Mississippi, between the Ohio and the Kaskaskia, is also a considerable stream. The rivers flowing into the Ohio and Wabash are generally of less volume than the smaller class of streams flowing into the Mis- sissippi, but several are navigable. Chicago river falls into Lake Michigan; it is formed by the union of its N. and S. branches about 1 m. from the lake. Both branches are deep (12 to 15 ft.), and in connection with the main river form a spacious harbor, which has been much improved by the extension of piers far into the lake. The S. branch is connected with the navigable Illinois at Peru by the Illi- nois and Michigan canal, 96 m. long. Not- withstanding the general uniformity of the surface, Illinois is not destitute of interesting scenery. The river bluffs contrast strikingly with the smooth prairies. The most remark- able of these elevations are on the Mississippi, and are from 100 to 400 ft. high. Fountain bluff in Jackson co. is oval, 6 m. in circuit and 300 ft. high ; the top is full of sink holes. Starved Rock and Lover's Leap are eminences on the Illinois ; the first mimed is a perpendic- ular mass of limestone and sandstone, 8 m. be- low Ottawa, rising 156 ft. above the river, and the latter a ledge of precipitous rocks some distance above Starved Rock. Nearly oppo- site Lover's Leap is Buffalo Rock, 60 ft. high, precipitous toward the river, but sloping in- land. The Cave in the Rock, in Hardin co., on the Ohio, presents on approach a vast mass of rocks, some resembling castellated ruins, and others jutting out in a variety of forms. The entrance to the cave, which is little above high water, is a semicircular hole 80 ft. wide and 25 ft. high, and the cave so far as explored consists of a chamber 80 ft. long, at the end of which is a small opening which probably leads into a second chamber. In the earlier days of settlement it was the abode of bands of rob- bers and river pirates. The unbroken surface of Illinois affords a drainage extending from the borders of Lake Michigan toward the west and southwest across the entire state. The post-tertiary clay and sands containing fresh- water shells of living species, found a few feet above the level of the lake, and forming its banks, indicate that at no remote geological period the land was somewhat less elevated than at present ; and the valley of the Illinois with its strongly marked terraced walls of limestone, so disproportioned to the small river that flows between them, would seem to owe its origin to mightier currents, and to point to a time when the great lakes found an outlet by this way to the Mississippi and the gulf of Mexico. The state has been de- scribed and mapped as one great coal field ; but as the arrangement of the strata has been more carefully studied, this statement is to be received with some modifications. Still, the prevailing rocks throughout the state are those of the coal measures. They occupy most of the country lying S. of a line traced from the mouth of Rock river E. to La Salle co., and thence S. E., crossing the line of In- diana. The formation covers a large portion of the W. part of Indiana, and stretches S. into Kentucky. Its W. margin is near the Missis- sippi river, along which a belt of the under- lying carboniferous limestone comes up, and cuts off the coal formation on that side. The included area, reckoned as one coal field, covers about 40,400 sq. m., of which 30,000 are in Illi- nois. The most important veins are from 6 to 8 ft. thick. (See COAL, vol. iv., p. 738.) The importance of the coal beds in Illinois is greatly enhanced by their position, conveniently near the Mississippi or the Ohio, and to the railroads, which traverse the state from N. to S. and from E. to W. ; and more than 2,000,000 tons per an- num are now mined in the state. The iron ores found in the coal measures are of little value. The N. W. corner of Illinois includes a portion of the great western lead-bearing belt. Though in Illinois hut a small district, compri- sing part of Jo Daviess co., contains the lower Silurian limestones in which the lead ores are found, the mines have proved so productive that the metal ranks as one of the important products of the state. Salt is chiefly a product of the southern section, and is found in springs about the head waters of Big Muddy river, Saline creek, and the Little Wabash. Sulphu- rous and chalybeate springs exist in several localities. The soils of Illinois are of diluvial origin, and it is probable that in the early geo- logical ages the whole state was a portion of the bed of a great lake. The prairie soils are deep, fertile, and rockless, and produce a luxu- riant growth of native grasses and vegetation, which formerly sustained countless herds of buffaloes. The largest of the prairies is that between the streams flowing into the Wabash and those which enter the Mississippi. This
