of Union, Johnson, Pope, and Hardin counties. To the north lie the lower lands of the Big Muddy and Saline river basins, and to the south the bottom lands of the Ohio, Big Bay, and Cache rivers. The axis of the ridge thus lies along an east west line in the northern portions of the four counties last named. A rectangle 70 miles in east-west extent and 12 miles in north-south dimension includes nearly all of the highlands of the Ozark Ridge in Illinois and considerable areas of lowlands along the stream valleys. The area, more than GOO feet above sea-level, is nearly 400 square miles in extent, and the total area, more than 500 feet in elevation, is about twice as large. The crest of the ridge, in at least four areas, rises above 700 feet, with the culminating peak. Williams' Hill in north eastern Pope County, rising to an altitude of 1,065 feet above sea-level, and more than 700 feet above the Ohio River 12 miles distant.
The Ozark Ridge rises somewhat abruptly from the border ing lowlands to elevations of 300 to 700 feet above the plains. Short, swift streams have eroded much of the area into rugged hills and ridges with numerous valleys. Some of these valleys are so narrow and steep that no bottom lands have yet been developed; others contain bottom lands of sufficient area to provide fertile farms. The ridges are in places too narrow and too rugged for cultivation, while in other portions, where stream erosion has not yet fully dissected the uplands, relatively large areas arc capable of profitable cultivation. The topog raphy, climate, and soil of certain portions of the Illinois Ozarks are well adapted to fruit growing, and orchards have been de veloped with profit.
A narrow spur ex tends southward from the main ridge in Jack son County into the northern portion of Alexander County be tween the Cache and Mississippi rivers. In the southern portions of Pulaski, Massac, and Pope counties, rugged hills and ridges are found between the broad flood plains of Cache and Big Bay rivers on the north and the Ohio River on the south. These detached highland areas arc a part of the Ozark system. Small detached hills and ridges of solid rock are also found in the Mississippi flood plain in Jackson County and in the lowlands near the Saline and Ohio rivers in Gallatin and Hardin counties. Sink holes and caves are found in some of the limestone regions of the Illinois Ozarks. The village of "Cave-in-Rock" in Hardin County is so named because of the presence of a large cave in the rocks along the Ohio River near the village.
From the western end of the Ozark Ridge in Jackson County, a long, narrow, rugged belt of limestone rocks extends northwestward between the Mississippi flood plain on the west and the coal-producing regions to the east, crossing the Mississippi River south of East St. Louis. It rises 300 to 400 feet above the Mississippi and 200 to 300 feet above the plains to the east. The ridge is 5 to 10 miles wide and is con tinuous throughout its extent of about SO miles in Illinois except for two gaps, each not more than 2 miles in width, made by the Big Muddy and Kaskaskia rivers. In this limestone ridge sink holes and caves are common, and under ground drainage through these sink holes and caves prevents the development of systematic valley systems on the surface.
This rugged belt has an elevation of 650 to 750 feet above sea-level. It forms the eastern edge of the extensive Ozark Highland which has its chief development on the opposite side of the Mississippi in southern Missouri. The narrow belt in Illinois has been severed from the main highland by the Mississippi River.
The topographic control of the Ozark Ridge on the courses of streams and on the location and direction of highways and railroads is very marked. No stream within the state crosses the highland in a north-south direction. Short, swift streams flow down the steep northern slope to the Big Muddy and Saline rivers. The rapid streams on the south slope of the main ridge carry their waters quickly to the sluggish Cache River and Big Bay Creek, which occupy an abandoned channel of the Ohio. No railroad traverses the Ozark region along an east-west line. Low passes are sought, for north-south lines, and at Tunnel Hill in Johnson County a railroad tunnel, 900 feet in length, has been driven through solid rock, High ways seek the lowest passes and the easiest grades which, at their best, are difficult of ascent.
Other rugged areas.—Near the junction of the Illinois and Mississippi rivers, a geological uplift has given rise to rugged lands in Jersey, Calhoun, and Pike counties. Just east of the mouth of the Illinois River, a few points have an altitude of more than ,S00 feet above sea-level. The rugged ridge of Calhoun County and southern Pike County is 700 to 750 feet above sea-level.
In the northwestern part of Illinois, including Jo Daviess County and portions of Stephenson and Carroll counties, is found the rugged land of the Driftless Area, which is more extensive in Wisconsin than in Illinois. "Mounds" and "knobs" are more characteristic of the topography of this region than ridges. Charles Mound, 1,241 feet above sea level, in Jo Daviess County near the state line, is the highest point within Illinois. These mounds rise 75 to 300 feet above the more level land of the region, and vary in size from a few acres to several square miles. The numerous mounds and well-developed drainage systems make this region one of varied topography.
These rugged areas of Illinois together with the river bluffs of the main streams, especially the Illinois, Mississippi, and Ohio, furnish a greater variety of interesting and picturesque scenery than is usually credited to the Prairie State.
Summary.—While Illinois is rightly considered as a part of a flat plain, its surface features are sufficiently extensive and varied to present striking contrasts of scenery and of land values. While the swamps and shallow lakes of the Illinois uplands have been drained and turned into fertile fields, there still remain numerous difficult and expensive reclamation projects along the flood plains of bordering and of state streams. Twenty-three of the forty-eight states of the nation furnish water which flows across Illinois or along the borders of the state. Populous commercial centers so located as to be subject to flood damage must ever apply the best methods of securing protection against the floods which come from time to time.