WEBSTER — THE ROCKFORD SHALES OF IOWA. IOI 



colored clay, which, at Hackberry, contains numerous hard, dark red, 

 ferruginous concretions, varying in diameter from one to four inches. 

 The lowest twenty-five feet of the forty-five foot stratum at Hackberry 

 is blue clay, which is mostly covered by a layer of shales. 



On Flood Creek, at Rudd, in. Floyd County, the shales are well 

 exposed for a short distance in the east bank. Here the following 

 section was taken : 



i. Drift and detritus 2 feet. 



2. Yellowish brown (sometimes shaly), thin-bedded lime- 



stone, containing several species of corals, Stromato- 

 pora, Sfiirifera, etc., which are not known to occur 

 in the shales at any other place, but which are more 

 or less common in the limestone in other portions of 

 the State 4 feet. 



3. Yellowish brown, argillaceous, shaiy limestone, con- 



taining some sand, and numerous species of fossils, 

 as P. woodmani, O. iowensis^ Luxonema, A. reti- 

 cularis, etc., and weathering to a yellow clay. This 

 division passes imperceptibly into No. 2 5 feet. 



4. Grayish-buff limestone, made up almost entirely of 



concretions of a harder and darker material, and 

 containing numerous Lamellibranchiata (none of 

 which are known to occur in the shales), with a few 

 specimens of P. woodmani and O. iowensis at the 



top, to the bed of the creek 9 y 2 feet. 



Total 20^ feet. 



In the bed of the creek, about one-half mile below the above local- 

 ity, a small quarry has been opened in limestone immediately below 

 number 4. Here measurements gave the following results : 



1. Yellowish-buff, thin-bedded limestone 3 feet. 



2. Thicker bedded, grayish-blue limestone 3 " 



Both divisions contain the same assemblage of fossils, most of which 



are Brachiopoda. Only one or two of the species occurring in these 

 beds are known to extend upward into the higher beds. 



In the west bank of this creek, three miles south of the above local- 

 ity, the shales are again observed. The beds here attain a thickness, 

 by estimate, of about nine feet, and are made up of thin-bedded, 

 somewhat friable, brownish-yellow, calcareous and argillaceous lime- 

 stones, which contain an abundance of Fistulipora occidens (?). 



Underlying the shales is a nine-foot stratum (not well exposed) of 

 limestone, which is apparently the equivalent of the concretionary lime- 

 stone of the Rudd section. 



In the extreme south-western part of Floyd County, and the south- 

 eastern portion of Cerro Gordo County, the shales are much thinner, 



