42 



GEOLOGY OF ERIE COUNTY 



more dense shales have strongly marked cleavage planes. At 

 intervals, in the vertical succession, are layers of calcareous 

 concretions. Many of these are septaria, and many are of huge 

 size. Septaria six feet in diameter and four feet thick are 

 numerous. The septaria seen in cross section are crossed by 

 series of radiating and concentric veins filled with white, black 

 and brown crystals of calcite. 



F. Houghton, Photo. 



Fig. 17. A typical Rhinestreet cliff, Eighteen Mile creek below Hamburg. 

 Note large concretions. 



The shale immediately about the large concretions bends 

 about them following the contours of the concretions rather than 

 the normal horizontal bedding plane of its bed. A few of the 

 concretions contain fossils. Two in the Eighteen Mile creek 

 cliffs contained huge fish remains. From one found by the 



