IOWA ACADEMY OF SCIENCES. 23 



The second stage is defined by the abundance of fragments, usually small, 

 of a hard, drab, unfossiliferous limestone of finest grain, often thinly bedded, 

 often finely laminated, the lamimo frequently being Hexed or contorted. 

 This limestone also is not found undisturbed in Linn county. 



The first stage is characterized by an abundant buff or brown matrix, the 

 fragments beiug sparse and small. Some of them are quartzose, belonging 

 like the matrix to the subjacent terrane. 



This subjacent terrane, locally called the Kenwood beds, consists of mas- 

 sive argillaceous and ferruginous buff and reddish-bi'own limestones, irreg- 

 ularly bedded, often Hexed and arched and passing horizontally and verti- 

 cally beneath into buff thinly laminated or shaly limestone, weathering into 

 slopes of marly clay. In these beds nodules of crystalline quartz with cal- 

 cite and angular fragments of the same are common. Beneath the buflf 

 shales which constitute the bulk of the Kenwood beds lies a layer of green- 

 ish or bluish fissile shale from a few inches to five feet thick. The upper 

 limestones ai*e usually involved, more or less in the Fayette breccia. The 

 total thickness of the Kenwood beds is nearly forty feet. The basal blue 

 shale in especial is believed to represent the horizon of the Independence 

 shales. The latter term, originally designating some sixteen feet of dark car- 

 bonaceous and grey fossiliferous shale pierced by a well near Independence, 

 may readily be extended, however, to include all the limestone and shale of 

 the Kenwood. The latter term is, therefore, used on-ly as a local synonym 

 for the Independence shales, of which it offers many natural sections, the 

 first discovered. 



Beneath the Kenwood beds in Linn county lies a Devonian terrane not 

 hitherto known, termed the Otis beds. Like the Kenwood beds, from which 

 it is somewhat sharply divided, the Otis limestone is remarkably constant 

 and uniform in its lithological features, some layers with special character- 

 istics being traced across the county. It consists of nearly pure non-mag- 

 nesian limestones, some macro-crystalline and some non-crystalline and 

 compacted of impalpable calcareous silt, often heterogeneous in texture, 

 often lying in heavy lenticular masses, passing into thin calcareous plates. 

 In all the numerous exposures of these beds from the Cedar River above 

 and below Cedar Rapids to near the Jones county line southeast of Spring- 

 ville, Hpirifcra subumbona (Hall) is found gregarious in a typical form dis- 

 tinct from the varietal form found in the Independence shales at Inde- 

 pendence. On the Buffalo and Wapsipiunicon rivers the numerous sections 

 of the Otis limestone are unfossiliferous. The Otis beds, whose total thickness 

 is thirty feet, include hard thinly-bedded magnesian limestone basal layers by 

 which they pass without unconformity into softer heavily bedded dolomitic 

 limestones, probably Silurian in age, provisionally called the Coggan beds. 



It is believed that the Devonian succession in Linn county will be found 

 to obtain elsewhere in the State where the lower strata of the system are 

 exposed. 



At Davenport, for example, the lower limestone out-cropping along the 

 Mississippi river from the city northward to Gilbertsville, thinly bedded, 

 arched and partially brecciated, is identical in appearance with the frag- 

 ments of the second stage of the Fayette breccia from Fayette to Cedar 

 Rapids. Under the saddles of its folds there emerges a brown ferruginous 

 limestone indistinguishable from the Upper Kenwood, whose horizon it 



