ON THE STOCKDALE SHALES. 



671 



readily distinguishable from any of the preceding Graptolite-zoues, 

 even at a distance of some yards. 



The entire thickness of this subdivision is seven feet nine inches, 

 and the subjoined details are given, as usual, in descending order : — 



ft. in. * 



Richly Graptohtic black shales, passing into muclstones above... 4 



Blue mudstones, with few Gi-aptolites 11 



Graptohtic shales 3 8 



Green mudstones 1 H 



Graptolitic shales 2 



Green streak. 



Graptolitic shales, passing into glaher-zon.Q below 1 2 



Total 



7 y 



The lowest part, one foot four inches in thickness, lying below the 

 green mudstones, is distinguished by the great abundance of Diplo- 

 graptus tamariscus, Nich., preserved in a state of semi-relief. As 

 this speci-es is tolerably abundant elsewhere, including the upper part 

 of the zone under consideration, we do not intend to separate this 

 lowest portion as a distinct subzone, especially as all the fossils 

 found in it occur in the rest of the zone ; but we call attention to 

 it, as a similar abundance of D. tamariscus is found on the same 

 horizon in other sections. 



As the shales of this zone are easily distinguished in other parts 

 of the gill, and present no particular variations, we need not give 

 a detailed description. Most of our fossils have been obtained from 

 the immediate neighbourhood of the Lower Bridge, from the angle 

 of the stream just above the high precipice a few yards above this 

 bridge, and from the bank just N.E. of the high precipice in the 

 moorland portion of the stream. These fossils are : — 



Monograptus convolutus, His. 



gregarius, Lapw. 



Clingani, Carr. 



crenularis, Lapw. 



communis, Lapw. 



Nicoli, Harkn. 



attenuatus, HopJc, 



argutus, Lapw. 



cyphus, Lapw. 



involutus, Lapw. 



Eastrites hybridus, Lapw. 

 peregrinus, Barr. 



Eastrites urceolus, Bichter. 



gemraatus, Barr. 



Petalograptus cometa, Gein. 



folium. His. 



ovatus, Barr. 



Retiolites perlatus, Nich. 

 Diplograptus Hughesii, Nich. 



tamariscus, Nich. 



raodestus, Lapw. 



Climacograptus normalis, Lapw. 

 Dawsonia campanulata, Nich. 

 Leptsena quinquecostata, M'Coy. 



Of these M. convolutus., His., is the most prominent form. It 

 does occur in the M-argenteus zone in considerable abundance, but it 

 is found here in a beautiful state of preservation and in great 

 abundance ; only one specimen of P. cometa has been found in this 

 gill. We name this zone the Zo7ie of Monograptus convolutus. 



(6) The succeeding blue mudstones, which we take as marking 

 the summit of the Middle Skelgill Beds, are seen on the footpath at 

 the Lower Bridge, near its summit. They are four feet in thickness, 

 and similar in lithological characters to the mudstones of the Fhacops- 

 glaher zone, but do not contain any band of calcareous nodules. 



2y2 



