from Penigent to Kirkbi/ Stephen. 75 



is obvious^ that it owes its existence to the accidental presence of beds of 

 shells (chiefly of the genus Producta)^ during the deposits of the great masses 

 of shale — that these shells supplied a considerable portion of the calcareous 

 matter — and that they also caused the precipitation or separation of the ferru- 

 ginous and pyritous matter^ and of the other constituents commonly found 

 together in these calliards. 



In the upper division (c) of the group here described, there is in some 

 places a band of coal : but as it is in general not more than a few inches in 

 thickness, it has never been worked to any profit*. 



5. Strong Post Limestone. Thickness nearly the same as the black marble 

 series (No. 3.), averaging about 30 feet. 



This group, in its mode of bedding, in its colour, and in the dark bands of 

 shale which alternate with the strata, nearly resembles the black marble system. 

 The beds are however stronger, thicker, and coarser ; and though generally 

 unfit for polishing, afford a beautiful material for the construction of door- 

 posts, small pillars, coignes, coping-stones, &c.f 



I have traced this group in the position here indicated, through the flanks 

 of Ingleborough, Penigent, and Whernside; all round the valley of Dent; 

 through the upper part of Garsdale ; and through a part of the chain of hills 

 between Wensleydale and Swaledale. There can, therefore, be no doubt of 

 its continuity through all the country bordering on the southern and central 

 part of the principal section. 



6. Alternations of Fissile Gritstone and Carbonaceous Shale. Greatest 

 thickness 150 feet; average thickness about 120 feet. The alternations are 

 indefinite ; but on the whole the group may be conveniently separated as 

 follows. 



(«.) Alternations of gritstone and shale ; the gritstone sometimes rising in 

 strong beds ; but more frequently micaceous and of a flaggy structure. 



(6.) Carbonaceous shale and gritstone with a band of coal ; also with two 

 thin bands of crow-limestone or calliard. 



(c.) Hard, brown, and light grey, micaceous grit, with bands of shale ; the 

 micaceous grit in some places highly fissile, and forming a good roofing slate. 



The most important bed in this group is the coal in division (6). It is ex- 



* I have been informed that works were formerly opened in this bed at Load Gill on the south 

 side of Dent, and also on the north side of Garsdale, but with very little success. 



t Attempts have, I believe, been made, but without success, to polish some of the darker beds 

 containing many very small encrinital stems. A small, dark-coloured, encrinital marble, found in 

 Derbyshire, and other parts of the carboniferous chain, is provincially called bird's-eye marble ; 

 and is occasionally found subordinate to the black marble group. 



L 2 



