72 Prof. Sedgwick on the Carboniferous Chain 



which occur here and there at the base of the series. In the same position 

 are rarely found some dark and nearly compact beds^, resembling the black 

 marble series, but unfit for use ; and in the prolongation of the longitudinal 

 section towards the north (for example^ near Ravenstonedale and Kirkby 

 Stephen), beds of reddish sandstone alternate with the lower portion of the 

 scar limestone, and the whole group begins to approximate to the type of the 

 Cross Fell chain*. 



There are no bands of coal subordinate to the limestone on the sectional 

 lines; but carbonaceous and bituminous matter are the colouring principle of 

 all the darker beds. In some instances this colouring matter is so unequally 

 diffused, that after a recent fracture, or on a polished surface, it appears in 

 the form of dark cloudy blotches upon a light grey base. It is this arrange- 

 ment of colours, arising out of the irregular diffusion of the bituminous matter, 

 which constitutes the beauty of some marbles in the North of England f. 

 Near the line of section, however, no beds appear in this limestone which are 

 fit for polishing, and very few indeed which are well suited to the commonest 

 domestic architecture. In general they have an irregular fissured or shaken 

 texture, which unfits them for such uses. It is, perhaps, hardly necessary to 

 add — that their prevailing colours are light grey or bluish grey, from which 

 they change, through every variety of shade, into dark blue, or bluish black 

 — that their mineral characters are such as link them to transition limestone 

 — and that they contain in great abundance corallines, encrinites, and all the 

 ^ ordinary well-known fossils of the carboniferous limestone];. 



The highest beds of this group often become impure, and, for about thirty 

 or forty feet, alternate with beds of sandstone and calcareous shale ; in this 

 way forming a gradual passage into the next superior group. 



2. Group of Sandstone and Shale. Greatest thickness 150 feet. 



The thickness of this group is extremely variable, being in some places not 

 more than twenty or thirty feet: but when it is best developed, it appears to 

 admit of the following subdivisions : — 



(a.) Dark-coloured shale, with nodules of clay iron-stone. 



* In various parts of the North of England, where the bottom beds of the scar limestone rest 

 immediately upon greywacke, they contain rolled pebbles of the inferior rock, and occasionally 

 pass into a coarse conglomerate form. (See Geol. Trans., Second Series, vol. iii. p, 10, &c. &c.) 

 This structure seems to have originated in the last feeble efforts of those causes which in other 

 places produced the great masses of old red conglomerate. 



t The Beetham Fell marble, near Milnthorpe in Westmoreland, is the most remarkable instance 

 of this kind, and it is subordinate to the great scar limestone. 



X Some of the rare corallines, described by the late Mr. Parkinson, were collected from loca- 

 lities near the line of section. See " Organic Remains," vol. ii. PI. VI. fig. 9. &c. &c. 



