70 



ME. J. E. MARK AND DR. H. A. NICHOLSON 



This is one of the most prominent bands in the gill, as the lines 

 of nodules present a very striking appearance, and as the whole 

 deposit is traversed by a series of strike-joints, along which it breaks 

 off in massive blocks, sometimes four or five feet in length each way ; 

 the overlying shales usually present a projecting cornice of jagged 

 appearance above the smooth face of the portion of the cliff which 

 is composed of these mudstones. Por these reasons, there is not 

 the slightest difficulty in tracing this band wherever exposed, and 

 there are few places where this hard blocky deposit is concealed by 

 detritus. Where the band comes down to the stream, at the point 

 of maximum disturbance produced by the strike-fanlt, namely in 

 the very high precipice in the moorland part of the gill, a number 

 of flat elliptical concretions, with a reticulated surface and a black 

 earthy appearance, were found by us in it. These concretions are 

 apparently formed of oxide of manganese, and they probably occur 

 in other parts of the gill, though we have not come across them. 



The fossils of this band are admirably preserved, like those of the 

 Uncrinurus-zojiG. They are : — 



Favosites mullochensis, Nick. ^' 



Etk., pin. 

 Phacops elegans, Boeck ^ Sars. 



, Tar. glaber. 



Cheirurus bimucronatus, Murch., 



var. acanthodes, var. nov. 



Cheirurus moroides, n. sp. 

 Harpes angustus, n. sp. 



judex, n. sp. 



Calymene Blumenbachii, BrongnU 

 Whitfieldia tumida, Balm. ? 



The new variety of Pliaco]^s is the most prominent fossil, and, 

 although not confined to this band, occurs more abundantly here 

 than elsewhere ; hence the name we have adopted for this band, viz. 

 the Zone of Phacops glaher. 



(5) The Graptolitic shales which have been alluded to as forming 

 a cornice above the P.-glaher zone in the precipices are seen about 

 halfway up the path which crosses the Lower Bridge, where the usual 

 gradual passage from the mudstones to the Graptolite-bearing shales 

 may be observed. This passage always takes place in the vertical 

 distance of two or three inches, and is due to the gradual develop- 

 ment of lamination-planes in the mudstones, which at the same 

 time begin to contain a few Graptolites, assume a darker hue, and 

 are not calcareous. These Grraptolitic shales above the glaher- 

 zone are very finely laminated, so that they break into thin pieces, 

 thus differing from the mudstones of the M.-argenteus and M,- 

 fimhriatus zones and of the Lower Skelgill Beds. "When much jointed 

 and cleaved, they break up into small rectangular pieces, but when 

 the divisional planes produced subsequently to deposition are less 

 marked, they afford tolerably large but thin slabs. The shales are 

 also less dark than those of the underlying Graptolitic zones, the 

 usual tint being a somewhat dark greyish blue instead of black, 

 though here and there black shales do occur. One of the most 

 noticeable features is the light olive-brown staining of the joint sur- 

 faces ; by this peculiarity, and by their fissile character, they are 



