10 CiEOUHiY OK ILLINOIS. 



vineyard may be made to grow, whose generous fruitage 

 will more than repay the expense and toil. 



But, leaving these topies, which belong rather to practi- 

 cal agriculture and horticulture than to geology, I pass to 

 notice some phenomena more particularly discernible along 

 the small streams between the Mississippi and Rock rivers. 

 There are a number of these large creeks and small rivers, 

 referred to in the county reports. Those crossing the face 

 of the country in an eastern or western direction, generally 

 have the strata along the north side of the stream, elevated 

 higher than those on the south side. In. some instances the 

 stream is the dividing line between an older and more re- 

 cent formation. The Cincinnati shales and limestones 

 often underlay the level prairies on the south side, up to 

 the very water's edge ; while the country on the north side 

 rises in rather bold outcrops of the Galena limestone. I 

 think the streams are oftener than otherwise the dividing 

 line between different groups and formations. 



Closely connected with this phenomenon is another. The 

 streams often seem to flow in fissures or cracks of the un- 

 derlying rocks. Slow upheavals, and slight contractions 

 in the cooling earth perhaps, made these fissures. In time 

 they filled partially, making the narrow bottoms and the 

 beds of the present streams. Slight faults were thus left, 

 which seem to be bounded by the streams, and fully account 

 for the difference of elevation on different sides of east and 

 west streams. / 



While speaking of the surface geology of the region be- 

 tween the two rivers, a few words as to the origin and for- 

 mation of the prairies, may not be out of place. 



The largest portion of this part of the State is prairie 

 land. In it all kinds of prairies may be seen, such as the 

 high upland prairies, the river bottoms or alluvial prairies, 

 and the low, wet swamp lands. 



There is quite a diversity of opinion as to the origin and 

 formation of these treeless and grass-covered regions of the 



