488 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



Doctor Norton recognized some of them as blocks of the Otis calci- 

 lutite. Fossils are few but typical. 



Exposure No. 3. — This outcrop is in Benton county on the left 

 bank of Cedar river in the northwest quarter of section 9, township 

 86 north, range 10 west, and is about two miles south and one mile 

 west of Brandon. The shale occurs in a re-entrant near the north 

 end of a precipitous cliff close to fifty feet high, called by Savage,^ 

 in his Benton county report, the Cedar river section. To the north 

 across a ravine is Long's quarry — both exposures are Cedar valley 

 limestone. In the re-entrant among the tumbled blocks of lime- 

 stone occurs the shale with its characteristic fossils. Three or four 

 feet of the shale are exposed at a height of about ten feet above the 

 water and separated from it by a gentle talus slope fifteen to twenty 

 feet wide. The re-entrant is twenty-five to thirty feet wide and be- 

 comes wider within where its walls are largely joint faces in the 

 limestone away from which the rock has slipped toward the opening 

 due to sapping. The material from this large well or cistern-like 

 hollow in slipping out has encroached on the shoreline in the form 

 of a small talus delta. Within the "well" the talus rises away from 

 the opening to the top of the cliff with a slope so steep as to be 

 climbed with difficulty. The rock in the walls of the "well" are 

 practically horizontal and but little disturbed. Between this expo- 

 sure and the ravine to the north, however, there is evidence of con- 

 siderable disturbance. Faulting here has brought up brecciated 

 Davenport beds almost to the top of the cliff. The position of the 

 ravine itself suggests a line of weakness. Brecciated blocks lying at 

 all angles, slicken-sided faces, distorted and obscure bedding, and 

 joints and fractures are some of the features which testify to the 

 stresses which accompanied the displacement. Moreover, the rocks 

 in the disturbed section are practically barren in comparison with 

 the very fossiliferous Cedar Valley beds a few yards to the south 

 as well as to the north across the ravine in Long's quarry. 



Summarizing the three exposures of the shale we may note that 

 they are alike in that they abut laterally against Cedar Valley lime- 

 stone ; in that the overlying beds are absent or unexposed, as far as 

 could be determined, while the underlying strata at each place are 

 inaccessible ; in that each is a sort of shale breccia containing an 

 admixture of blocks and fragments of sub-Cedar Valley limestones; 

 and in that each carries the typical Independence fossils. 



•Iowa Geol. Survey, Vol. XV, pp. 180, 181, 1905. 



