84 GEOLOGY OF ILLINOIS. 



its Eock river valley, and the enterprise and wealth of its grove- 

 besprinkled city of Eockford, it would puzzle a jury to decide which is 

 the most desirable county. 



Geological Formations. 



The geology of Winnebago county is of the simplest character. First, 

 there is the usual Quaternary deposits, consisting of sand, clays, gravels, 

 boulders, subsoils and alluvium. After these, the three well known 

 divisions of the Trenton limestone outcrops along the streams and hills, 

 and show themselves in the railroad cuts, wells and quarries in different 

 parts of the county. These are the Galena, Blue and Buff' limestones 

 of the Western Geologists. A perpendicular section, as near as we can 

 construct it, exhibits the following strata : 



Quaternary Deposits. Average depth about 15 feet. 



Galena Limestone 96 " 



Blue Limestone 35 " 



Buff Limestone 45 " 



The measurements of the limestones are made at actual worked out- 

 crops'. At no place could we discover the St. Peter's sandstone, although 

 it must come well towards the surface about Beloit and Eockton. 

 Neither could we discern remains of the Cincinnati group, although the 

 thickness of the Galena would indicate that patches of it might exist. 

 We believe, howevej?, that the Trenton limestones are the only ones at 

 any place exposed or dug into in the county. 



Surface Geology. 



Alluvial Deposits. The usual alluvial bottoms exist along the Eock, 

 Pecatonica, and Sugar rivers. These are from one to five miles wide. 

 On the two latter the deposit is deep, black, fat, and rich, supporting in 

 places a heavy growth of timber, and where cultivated affording the 

 usual superior Indian corn land of flat river bottoms. The deposit 

 along Eock river is not so rich, being composed more of sands and clays, 

 with occasional patches and strips of the fatter soils. 



Loess. Some of the bluffs along Eock river are in part composed of 

 loess clays, in which no fluvatile shells were noticed. This formation, 

 however, is of quite limited extent. 



The Drift Proper. The drift, now the subject of grave discussion 

 among the geologists, is very largely developed in Winnebago county. 

 It is composed of loose detrital matter, often of considerable thickness, 



