ON THE STOCKDALE SHA.LES. 



669 



from the base to this zone iuclusive, and the succeeding mudstone 

 bed is brouofht aorainst the Ashofill Shales. 



The fossils enumerated in 

 by us in this black band : — 



Monograptus argeuteus, Nich. 



gregax'ius, Lapw. 



leptotheca, Lapw. 



Nicoli, Harkn. 



Clingani, Carr. 



crenularis, Lapw. 



cyplms, Lapw. 



convolutus, His. 



involutus, Lapw. 



attenuatus, Hopk. 



argutus, Lapw. 



Hisingeri, Carr. 



tenuis, Portl. 



Kastrites peregrinus, Barr. 



the ensuing list have been discovered 



Rastrites hjbridiis, Lapw. 



• urceolus, Rlchter. 



gemmatus, Barr. 



Diplograptus siuuatus, Nich. 



tamariscus, Nich. 



Hughesii, Nich. 



modestus, Lapw. ? 



Petalograptus ovatus, Barr. 

 Cliraacograptus normalis, La'pw. 

 Discinocaris Browniana, Woodw. 



g'gas, Woodw. 



Dawsonia carapanulata, Nich. 

 Orthoceras araneosum, Barr. 



The beautiful M. arr/enteas, Nich., which used to be readily pro- 

 curable from this band, appears to be entirely confined to it, and 

 although the bed is so thin, its fauna is so rich, and the bed such 

 a remarkable one in every particular, that we consider it worthy of 

 being ranked as a distinct zone, which we term the Zone of Mono- 

 graptus argeuteus. 



(4) Once more we return to the Lower Bridge, and proceed to 

 examine there the mudstones into which the M.-argenteus Zone 

 passes upward. 



What we have said of the lithological characters of the Encrinurus- 

 punctatus Zone is applicable here, except that the calcareous nodules, 

 instead of being spread at nearly equal distances throughout the 

 deposit, are chiefly collected towards its centre. Otherwise, we 

 meet with the same blue mudstones, with bedding-planes tolerably 

 far apart, and the intervening rock breaking with the same difficulty 

 as that of the Encrinurus-zon.Q. The calcareous nodules weather 

 out leaving a brown or chocolate-coloured earth, which is also fre- 

 quently found along the bedding-planes. The following details of 

 these mudstones, given in descending order, and measured at this 

 foot-bridge, are generally applicable to the horizon at other parts of 

 the gill:— 



ft. in. 

 Blue mudstones (passing up into Graptoli tic shales) ... 4 

 Nodule-band. 



Blue mudstones 



Nodule-band. 

 Blue mudstones 



Nodule-band. 

 Blue mudstones 



Nodule-band. 

 Blue mudstones 



Nodule-band. 

 Blue mudstones 



Q. J. G. S. No. 176. 



6 



10 



Total. 



. 6 



. 12 1 

 2t 



