THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS XXvii 



exposure to erosion its streams have reached the Hmit of their 

 development, and run usually through deep valleys with rather a 

 swift current, mostly unobstructed by rapids or falls. As a conse- 

 quence of this perfect drainage and rapid flow, the surface waters 

 quickly escape to the Mississippi ; but as the streams are fed to a 

 considerable extent by springs flowing from the limestone rocks, 

 they rarely are completely dry. There are no lakes, swamps, or 

 other reservoirs for the sedimentation of the surface waters, and 

 the streams are consequently easily roiled by storms, in the intervals 

 of which, however, the water is comparatively clear. 



This driftless area of northwestern Illinois contains about 1 ,030 

 square miles, and includes all of Jo Daviess count3^ tw^o thirds of 

 Carroll county, and a part of Stephenson. The surface is rolHng and 

 somewhat broken, with a general elevation varying between 700 

 and 1,000 feet, but rising in mounds and fiat-topped hills to the 

 highest point in the state, an elevation known as Charles Mound, 

 in Jo Daviess county, 1,257 feet above the level of the sea. The 

 surface rock of this district is mainly Trenton limestone, with 

 Cincinnati shales and Niagara limestone capping the higher hills. 



The principal streams of this region are Galena River to the 

 north and Apple and Plum rivers farther south. Many additional 

 smaller streams run down from the hills and bluffs to open directly 

 into the Mississippi. 



GALENA RIVER 



Galena River, called Fever River on many maps, rises chiefly in 

 La Fayette county, Wisconsin, which state contains also nearly 

 half the 390 square miles of its drainage basin. It runs with a 

 rather rapid course through the hilly country of w^estern Jo Daviess 

 county, often over a rocky bed, becoming comparatively broad and 

 sluggish as it crosses the Mississippi bottoms west of the town of 

 Galena to empty into the Mississippi River. 



APPLE RIVER 



Apple River rises in Lafayette county, Wisconsin, and flows 

 southeast, then southwest and finally south, emptying into the 

 Mississippi in northern Carroll county, Illinois. It has a length of 

 about 45 miles and drains an area of possibly 250 square miles. It 

 crosses the state-line at an elevation of about 950 feet, while its 

 mouth has an altitude of only 588 feet. In Jo Daviess county, the 

 upper channel of the river is narrow and the banks are steep and 

 150 to 200 feet high. In the lower part, the valley becomes broader 



