ON THE STOCKDALE SHALES. 



661 



at the summit. Immediately above this is a very tough bed, one 

 foot thick, consisting of an impure, compact limestone, containing 

 flocculent dark-grey patches, giving it a mottled appearance, and 

 holding a considerable quantity of iron-pyrites. There are no sub- 

 sidiary planes of deposition in this bed, which breaks with extreme 



Fig. 1. — Section across SJcelc/ill. (Scale 15 feet to 1 inch.) 



~As1igiU Shales 



difficulty, with a somewhat hackly fracture. At this point we have 

 obtained no fossils, but a few yards above the Lower Bridge, at a 

 spot presently to be described, there are a fair number of fossils, 

 which are obtainable with difficulty, the most abundant being a new 

 species of Atrypa, on which account we propose to term this bed 

 the Zone of Atryijci flexiiosa. 



(2) Immediately over this hard limestone band are bluish-black, 

 rather flaggy and somewhat calcareous shales, resting with perfect 



