SANDSTONE, SHALE, AND COAL. 109 



Beneath the blue limestone, we find a series of beds, correspond- 

 ing with what are usually termed coal measures. These consist of 



SANDSTONE, SHALE, AND COAL. 



This series (marked i) is usually of great thickness, compri«ii]g 

 the whole of the regular strata above the great beds of aluminous 

 schistus, in the third range of our alum hills ; and the principal part 

 of these strata, in the first and second, viz. all those beds that inter- 

 vene between the blue limestone and the schistus. It is unnecessary 

 to point out the geographical limits of these beds more particularly, 

 as they extend throughout the whole of this triple range of hills, from 

 the oolite chain to the vale of the Tees. 



This member of our strata consists of an alternation of sandstone, 

 shale, and coai^ to which also we may add ironstone, for this some- 

 times holds a conspicuous place among the other beds. It would be 

 vain to attempt to give an exact enumerationordescription of all these 

 strata, or even to subdivide the series ; for we find here a gi-eater 

 number of transitions and changes, and more diversity in the number, 

 order, and character, of the beds, than in any other member of our 

 strata. The same bed, as it respects geological position, is in one 

 place, a solid sandstone ; in another, contains nothing but shale ; and 

 in a third, presents alternate layers of both; the transitions being 

 frequent, and often sudden. The coal is subject to the same varia- 

 tions. In one spot, you will find numerous thin seams running in 

 the shale ; in another, a single seam; and in others, none at all. Some- 

 times the shale and coal predominate in the higher part of the beds, 

 and sometimes in the lower part ; and not unfrequently the sandstone 

 almost excludes both; beds of schistose sandstone usurping the place 

 of the shale. Hence, when we have noticed the order of the beds in 

 one place, we cannot calculate upon finding the same series in another 



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