ALUM SHALE. 13& 



shells, and in some instances are so highly calcareous as to form a 

 kind of ferruginous limestone. In most places, however, they con- 

 tain a large proportion of iron, Avhich some have estimated at from 

 30 to 60 per cent ; an estimation perhaps beyond the truth. Silex 

 and alumine also enter into the composition of the stone. Quantities 

 of the ore have been collected, and conveyed to Newcastle to be 

 smelted at the founderies. 



The number of the ironstone beds and the intervals between them 

 are greatly diversified. In some places, we find only 3 or 4 seams ; 

 in others, 13 or 13, if not more. Some of the intervening beds of 

 shale are only a foot or two in thickness, while others are three or 

 four feet. Here the shale begins to lose its fine grain and smooth 

 surface ; becoming rather rough and sandy, with some specks of mica. 

 Where the shale comes in contact with the ironstone, it is often 

 partially indurated, through the effect of the iron. 



In giving the series of beds at Boulby, we have estimated these 

 ironstone seams (No. 9) at 15 feet in thickness ; but they often occupy 

 more than double that space, particularly where the seams are very 

 numerous. As these beds rise up at Kettleness, we may denominate- 

 them, by way of distinction, the Kettleness beds. 



The next part of the strata (No. 10), consisting of shale, with 

 SOME IRONSTONE NODULES, may be described in a few words. It is 

 a continuation of No. 9, but with a smaller proportion of ironstone; 

 the latter usually presenting only a few scattered nodules, or strag- 

 gling rows of nodules. We have stated this member of the Boulby 

 series at 40 feet; but where the ironstone seams are very numerous, 

 so as to occupy a large space, its dimensions are proportionally 

 reduced. This part of the series and the former are so connected, 

 that where the shale predominates, the ironstone is scanty; and where 

 the ironstone abounds, the limits of the shale are contracted. We 

 might therefore have considered both as forming one bed, consisting 



