666 301. J. E. MARE AXD DR. H. A. NICHOLSON 



This is the greatest thickness of these beds which we have mea- 

 sured between the strike-fault and the overlj^ing blue mudstones. 

 In other parts of the stream the strike-fault approaches nearer to 

 the mudstones and, indeed, frequently cuts out these black Graptolitic 

 shales altogether. The passage from the Graptolite-bearing beds 

 into the blue mudstones above is complete. The Graptolites become 

 much scarcer about two inches from the summit of the black beds, 

 and at the same time the blackness of the rock diminishes, until, 

 when the last Graptolites are seen, the rock has assumed a greyish- 

 blue colour, and its hardness has increased considerably. 



The group of Graptolitic shales we are now considering may be 

 seen at several points in the wood above the bridge, and in most 

 cases the passage can be traced into the blue mudstones above. At 

 the great cliff just above the foot-bridge the strike-fault has cut out 

 these beds and brought the overlj'ing blue mudstones against the 

 Atrypa-jiexuosa Bed, but on the other side of the dip-fault which 

 bounds the ]S".E. side of this cliff the shales are again seen, though 

 greatly crushed at the base. Many fossils, in an admirable state, 

 may be obtained near an adit which has been driven into the shales, 

 a little below the top of the wood ; and at the end of the wood, 

 where we emerge upon the moorland, the strike-fault is seen on the 

 left bank of the stream, where the shales are crushed into a mass 

 of black mud with ferruginous stains, immediately above which the 

 blue mudstones are seen in the cliff. Higher up the stream, the 

 Graptolitic shales below these mudstones are cut out, except at the 

 promontory on the right bank of the stream just below the Upper 

 Bridge. Here the shales are seen in a very crushed state on the 

 north-east side of the promontory, succeeded, as usual, by the blue 

 mudstones. 



The group of shales we have above described is distinguished from 

 those we have already considered, and from others which yet re- 

 main to be described, by lithological and palaeontological characters. 

 The beds are extremely dark, generally almost or quite black, and 

 though earthy are yet hard, and break into rather massive pieces. 

 The}^ are more cleaved than the shales below, and as the Graptolites 

 are chiefly found along bedding-planes separated from one another by 

 an inch or two of rock in which fossils are scarce, they do not break 

 into quite such thin slabs as do the shales of the B.-confertus Zone. 

 Several narrow lines of pale green mudstone occur here and there, 

 and in these Graptolites are very seldom found, though they are not 

 entirely absent. Pyrites occurs abundantly both in nodules and in 

 irregular patches along the bedding-planes, and, as a result, the joints 

 and cleavage-planes are usually stained a very deep brown. 



The fossils usuallj^ occur in a state of high relief, and are mostly 

 pjTitous and of a golden colour, though sometimes they are graphitic 

 and silvery when first obtained, ly^ost of the following fossils are 

 readily found wherever these shales occur in the stream : — 



