2 If GEOLOGY OF ILLINOIS- 



navigation by slack water dams from Rock Island to Lake 

 Horicon, thence across to Lake Winnebago, and thence 

 down Eox river in Wisconsin to Lake Michigan, is not only 

 a feasible project, but is full of interest to the people of this 

 valley and to the whole North-west. It will thus be seen 

 that Rock river and its valley, in their present and pros- 

 pective resources, salubrity of climate and beauty of loca- 

 tion, have not their equal in the State, or perhaps in the 

 nation. The geological formations along the stream are 

 also of an interesting character. The section of the river 

 bluffs herewith presented, and the following county reports, 

 contain detailed descriptions of these formations. 



At Beloit and Rocktoii the dull, yellowish earth-colored 

 buff limestone, with its bands of dark blue, is the surface 

 rock ; half way to Rockford this formation sinks below the 

 upper division of the Trenton; three miles above Rockford, 

 and at the city, the warm cream-colored Galena, limestone 

 outcrops in the river bluffs to the highth of one hundred 

 feet; lower down the Galena gradually thins out, until the 

 buff again comes to the surface in a low axis at Byron. 

 Eroin Oregon to Grand DeTonr the castellated hills of the 

 St. Peters' sandstone, shining white, brown, and flame- 

 colored in the sun light, and rising to an elevation of nearly 

 two hundred feet, form striking and picturesque objects in 

 the landscape; below these the solid Lower Magnesian 

 limestone probably forms the floor of the glancing river. 

 At Dixon two divisions of the Trenton may be examined 

 almost side by side for some distance; at Sterling the green 

 and blue shales of the Cincinnati group, and the chert-banded 

 and dendrite-speckled Niagara limestone outcrop heavily in 

 the same quarry; from Sterling to Erie, and even lower 

 down, the Niagara continues in the bed of the river and in 

 its banks, a low outcrop, changing before it runs under the 

 Coal Measures into a softer, whiter, iiiier grained stone, for- 

 merly called the LeClair limestone ; from a few miles below 

 Erie to Camdeii, the gently rounded hills and black lime- 



