CARBONIFEROUS SYSTEM. 277 



replaced by arenaceous shales, three feet. In the vicinity 

 of Panora a remarkable set of beds is associated with this 

 horizon, consisting of thin bedded very compact sandstone, 

 with thin interrupted coaly partings, enclosing a massive 

 brecciated layer with Prodactus muricatus, P. cequicostatus, 

 Clwnetes mesoloba, Atliyris subtilita, Petrodus; the whole 

 making a thickness of twenty feet. 



No. 19. Blue, more or less arenaceous indurated shales; 

 fifteen to twenty -five feet. Near the base is found a band of 

 dark blue clays, sometimes with pyritiferous nodules, in 

 which great numbers of Aviculopecten rectilateraria and 

 imperfect remains of ferns occur. This horizon may be seen 

 in the fine exposures on the South Raccoon river, on the 

 line between Dallas and Guthrie counties, and on the 

 Middle Raccoon river, above the mouth of Mosquito creek. 



No. 20. Light gray, soft sandstone; two and a half feet. 

 On the Middle Raccoon river above Mosquito creek. 



No. 21. Variegated, red, gray, and blue shales in alter- 

 nating layers, more or less arenaceous, and capped by thin 

 bedded micaceous sandstone; forty to sixty feet. This 

 portion of the section is finely exhibited in the exposures on 

 the Middle Raccoon river, above the confluence of Mosquito 

 creek, as is also the following Bed, No. 22, where these 

 argillaceous deposits have a much greater thickness than 

 elsewhere observed. Indeed, at some localities the argill- 

 aceous material is entirely replaced by laminated, more or 

 less micaceous, arenaceous shales and soft sandstone, as 

 shown in the exposures on the South Raccoon above the 

 confluence of the Middle Raccoon river. On Butler's branch, 

 near Adel, a similar arenaceous deposit is found in this 

 horizon, which has apparently replaced all the intervening 

 strata, and rests immediately upon the carbonaceous shales 

 overlying the Panora coal, (Bed No. 8). 



No. 22. Alternating layers of variegated shales, red, blue, 

 and chocolate colored, indurated, with arenaceous bands, 

 probably thirty to fifty feet; on the Middle Raccoon, near 

 the Dallas and Guthrie county line. 



