224 A POPULAR SKETCH OF THE 



Gritstone 



Shale, with ironstone 



Coal 



Shale, with coal 



Gritstone 



Shale 



Coal 



Gritstone 



Shale, with coal 



Gritstone 



Shale, with coal 



Gritstone 



Shale 

 Gritstone 



Shale 



Shale with limestone, 

 Limestone, with shale 



Limestone. 



The alternations, more especially of the upper part, are of course 

 much more numerous than are marked here ; but this will serve 

 just to give a rough notion of the relative proportions of the differ- 

 ent materials in the different parts of the series. 



Upon examining the rocks composing this series over the whole 

 district, and by attending, not only to the differences in the size of 

 their masses, but to their other characters, we are enabled to insti- 

 tute four divisions in this complex group, which are those given 

 before, (p. 223), and which will now be briefly described. 



6 — The Coal Measures, 



are the upper portion of the carboniferous group, and consist of 

 very numerous alternations of thick beds of shale (called, also, bind 

 and clunch), sandstone or gritstone, coal, and ironstone. The shale 

 is a slaty indurated argillaceous earth, varying in colour from light 

 grey to black, and treads down when exposed to the weather into 

 a soft unctuous clay. It lies in very thick beds, (each mass being 

 generally but one bed, which is sometimes sixty feet thick), com- 

 posed of very regular and almost innumerable laminae, marking the 

 gradual nature of its deposition. It is generally jointed, or divided 

 by vertical planes, very regularly, the joints being some yards apart, 

 frequently parallel to each other, and crossed by other similar ones 



