222 



GENERAL GEOLOGY. 



part of the State, although the two points are two hundred 

 miles apart. 



Vegetable Remains. Although Br. Owen reported some 

 years ago the discovery of the vegetable genera Lepidoden- 

 dron and Catamites in the sandstone division of this formation 

 in southeastern Iowa, subsequent careful search has failed to 

 detect any trace of such remains in that sandstone, and it is 

 therefore believed that they were observed in the sandstone 

 of the Lower coal-measures, which closely resembles that of 

 the St. Louis limestone formation in its lithological characters, 

 and is frequently found exposed in the same neighborhood 

 with it. This supposition is the more probable since he 

 reports two divisions of the concretionary limestone, identical 

 in character, with a series of sandstone layers between them. 

 The existence of more than one of these we have been unable 

 to verify. The only remains of vegetation yet known to 

 exist in this formation consists of a few inches of carbon- 

 aceous shale found between layers of limestone near Pella, 

 and a few fucoid-like markings upon the limestone strata 

 there. 



5. CONCLUDING REMARKS UPON THE SUB-CAR- 

 BONIFEROUS GROUP. 



In Iowa, the distinguishing lithological character of the 

 Sub-carboniferous group is its limestones. These are both 

 common and magnesian limestones; the former largely pre- 

 dominating. The sandstones of the earliest epoch are fine 

 grained, which seems to indicate that the waters in which 

 they were deposited were without strong currents. In the 

 Burlington and Keokuk limestone formations, as seen in 

 Iowa, sandy material is very rare, but among the strata of 

 the St. Louis limestone, we find the first clear grit or coarse 

 sandstones. From and after this epoch the coarse sandstones 

 prevail, and sometimes even exceed any other strata in aggre- 

 gate bulk. In southern Illinois and in some parts of 

 Kentucky, the Chester limestone formation is largely made up 



