308 C. LA.PWORTH ON THE MOEEAT SEEIES. 



Leptograptus, survivors from the Glenkiln Shales, all become ex- 

 tinct before we reach its highest beds. The allied genera Climaco- 

 graptus and Diplograptus are all that remain to link on the richly 

 varied forms of the Glenkiln beds to the highly prolific but mono- 

 tonous fauna of the Birkhill Shales. 



(a) Lower Hartfell. 



The Hartfell Shales fall naturally into two mineralogical subdivi- 

 sions — a lower group of dark fossiliferous shales, and an upper group 

 of pale barren mudstones. 



The Lower Hartfell is essentially a homogeneous mass of black 

 carbonaceous flags and slates, more or less fossiliferous throughout. 

 There occur, however, numerous intercalated seams of pale-coloured 

 argillaceous matter, sometimes hard and flinty, at other times soft 

 and easily disintegrated, and invariably destitute of all trace of 

 organic life. The distribution of these unfossiliferous beds allows 

 us to recognize three successive mineralogical subdivisions, which 

 form also the three palseontological zones of Climacograptus Wilsoni 

 (Lapw.), Dicranograptus Clingani (Carr.), and Pleurograptus linearis 

 (Carr.). 



i. Zone of Climacograptus Wilsoni (Lapw.) (fig. 27). — This zone 

 attains its most perfect development and most satisfactorily exhibits 

 its relationship to the beds above and below it in the North Cliff at 

 Hartfell Spa. Its basal beds run in a straight line for forty or 

 fifty yards along the steep slope immediately above the mineral 

 spring, distinctly overlying the soft yellow mudstones of the Glen- 

 kiln, and as clearly supporting and passing up into the main mass 

 of the Hartfell Shales. The zone forms a long projecting cornice ; 

 its strata dipping into the face of the cliff at an angle of about 40°. 

 They are wholly free from complication by fault or curvature, and 

 are all in such a position as to admit of a thorough investigation. 



The prominent appearance of this cornice, and its freedom from 

 the accidents which have befallen the surrounding beds, is due to the 

 presence of a bed of siliceous flags about 11 feet in thickness, simi- 

 lar in all respects to those so frequently adverted to in our descrip- 

 tion of the Glenkiln Shales, of which, indeed, it is the final band. 

 Like them it is highly resistant of atmospheric influences, but ulti- 

 mately weathers into cuboidal fragments. The bed upon which it 

 reposes is one of the dark, greyish-black flaggy shales of the Glen- 

 kiln division, which in its turn passes downwards into a great 

 thickness of soft yellow mudstone. These three beds are all of 

 Glenkiln age, the Hartfell Shales commencing immediately above 

 the siliceous band. 



This last is succeeded by a grey band of about a foot in thickness, 

 which passes upwards into 2| feet of soft black flaky mudstone 

 shales, separating under the hammer into large flakes or irregular 

 plates. These contain numerous narrow seams of shale of an open 

 texture, with a coarse ashy feel, and spotted superficially with white 

 or cream-coloured specks of foreign matter. The following 3 feet 

 of strata show few of these coarser lines, and the laminae are thinner 



