ON THE STOCKDALE SHALES. 



667 



Monograptus fimbriatus, Nich. 



gregarius, Lapw. 



tenuis, Portl. 



attenuatus, Hopk. 



Sanclersoni, Lapw. 



leptotheca, Lapw. 



triangulatus, Harkn. 



cyphvis, Lapw. 



Rastrites peregrinus, Barr. 

 Diplograptus tamariscus, Nich. 



Diplograptus sinuatus, Nich. 



Hughesii, Nich. 



• modestus, Lapw. ? 



vesiculosus, Nich. 



Petalograptus ovatus, Barr. 



ovato-elongatus, Kurck. 



Cliraacograptus normalis, Lapw. 

 Dawsonia eampanulata, Nich. 

 Discinocaris, n. sp. 

 Orthoceras araneosura, Barr. 



The above is a complete list of all the fossils found in these shales 

 in the gill. The first-named occurs everywhere in the zone in great 

 abundance, and usually in a beautiful state of preservation, and we 

 have met with it in no other beds either above or beneath. We shall 

 therefore speak of these shales as composing the Zone of Monograptus 

 Jtmhriatus. 



Monograptus gregarius, Jjfx^w., Bastrites peregrinus, Barr., Petalo- 

 graptus ovatus, Barr., and P. ovato-elongatus, Kurck, are all abun- 

 dant, and we frequently find beds covered with a confused mass of 

 Monograptus attenuatus, Hopk. Daivsonia eampanulata, Nich., is 

 often found in groups. We have only seen one or two doubtful 

 examples of Diplograptus vesiculosus, Nich. It is to be noted that 

 the genus Rastrites, which appears so abundantly in this horizon, 

 has never been found by us in any of the Lower Skelgill Beds. 



(2) Above the Zone of Monograptus Jtmhriatus we find a more 

 or less continuous section of the Middle Skelgill Beds all the way 

 between the two bridges ; and the observations made at the Lower 

 Bridge may be frequently checked by an examination elsewhere. 

 The sections below the Lower Bridge are less continuous, but here 

 and there high clifi's occur, showing a good development of the 

 various subdivisions. The blue mudstones succeeding thefimhriatu^- 

 zone are seen at the bottom of the path which crosses the Lower 

 Bridge. They are five feet in thickness, and pass downward in the 

 manner described into the M.-Jimbriatus beds. At the summit a 

 similar passage is traceable into a thin black Graptolitic band. 



The blue mudstones are hard, somewhat cleaved, grey-blue beds, 

 with prominent bedding-planes some distance apart. The rock is 

 somewhat calcareous, but the carbonate of lime has been mostly 

 collected into a series of extremely tough nodules, which have 

 weathered out along the clifi-faces, and show as a series of rust- 

 stained holes. The following measurements were taken at the 

 Lower Bridge, and show the variations in the band, the section 

 being a descending one : — it in 



Blue mudstones passing into Graptolite-shales above ... 1 

 Nodule-band. 



Blue mudstones 10 



Nodule-band. 



Blue mudstones 1 



Nodule-band. 



Blue mudstones 7 



Nodule-band. 



Blue mudstones 7 



White streak. 

 Blue mudstones, passing into il/".-/»j6mi{z^s beds 1 



Total 5 



