CARBONIFEROUS SYSTEM. 219 



all the strata. Also by the breaking up of that limestone 

 into angular fragments, which have in many cases become 

 re-cemented together by similar limestone material, forming 

 the breccia before referred to. r The most of this disturbance 

 seems to have prevailed during the deposition of the upper 

 division and to have commenced with its beginning, for at 

 Keosauqua we find angular fragments of the limestone 

 imbedded in the upper layers of the sandstone of the middle 

 division, while the limestone strata above it retain their 

 continuity. The slight local distortion of the strata of this 

 formation is shown in the accompanying sketch of an 

 exposure on the right bank of the Des Moines river, half a 

 mile above Keosauqua. The upper and middle divisions 

 only are shown in the sketch, but the extreme upper part of 

 the lower division exists at the water's edge there, where it is 

 brought up by one of the slight folds. At that point instead 

 of being as usual, magnesian, it is nearly pure limestone. 



Economic Value. The upper division, consisting as it does 

 of almost pure carbonate of lime, furnishes excellent mate- 

 rial for quicklime, even when it is so concretionary and 

 brecciated that it will not serve a good purpose for building 

 material. When quarries are well opened in it the layers 

 are usually found to be sufficiently uniform for common 

 purposes, and sometimes massive, as they are in the north- 

 western part of Van Buren county, where large blocks were 

 formerly quarried for use in the now abandoned Des Moines 

 river improvements. At several points in the vicinity of Pella 

 in Marion county, as well as elsewhere, the upper laj^ers 

 of the upper division are rather thin and regularly bedded, 

 while the lower layers of the same are uniform and thicker, 

 and furnish some of the best quality of limestone for dress- 

 ing into all desirable forms for building purposes. Wherever 

 the strata of the upper division are exposed they furnish 

 good material at least for common masonry and for lime.* 



* Some layers of this division having a very compact texture have lately been tested 

 for lithographic purposes, with results thus far only partially satisfactory. Further 

 trial is neeesgary to fully test its value, and a eompany has been formed for that 

 purpose. 



