84 Olstrvations on the Geology 



complete success. After perforating the whole of tlie s\ihjace'.;t 

 limestone rock, they bored through a lower bed, which Mr, G. 

 described to me as a dark-coloured argillaceous shale with oc- 

 casional hard stones which he considered as loose whinstones. 

 I have unfortunately mislaid the note respecting the absolute 

 depth of this bed given me by Mr. G., but I think it was not 

 less than 130 yards, and the whole depth of the upper good 

 workable coal not less than 260 yards. At a greater depth under 

 this was another valuable coal bed. I mention this fact, as it is 

 of some geological importance, and is, I believe, the only instance 

 in the district of coal having been actually found by boring through 

 the magnesian limestone. Some of the mining agents atNewcastle, 

 who were unacquainted with the above circumstance, gave me 

 their decided opinion that the coal cropped out, or was cut off 

 bv dykes, before it reached the limestone of Sunderland. It may 

 perhaps deserve future inquiry, whether this thick bed of shale 

 above mentioned be not a continuation of the aluminous schistus 

 from the Cleveland Hills on the south. 



The limestone of Building Hill near Sunderland and at Fulwell 

 is particularly deserving notice, from the remarkable configura- 

 tions which it presents. 



The beds at the former place are of considerable thickness : the 

 limestone is imperfectly crystalline, is of a yellowish-brown co- 

 lour, and yields a foetid smell when struck with a hammer, being 

 that species called by mineralogists swinestone. It contanis 

 nearly the same proportion of magnesia as that of Brecdon in 

 Leicestershire, first analysed by Mr. Tennant. 



The limestone in some of the beds is divided into small cells 

 uniting with each other, and pretty regularly arranged : this has 

 received the appellation of honeycomb limestone, a name which 

 conveys a tolerably correct idea of its appearance. 'A superficial 

 observer might suppose from the form that this was the organic 

 remains of some species of madrepores ; but it is evidently the 

 result of a tendency to crystalline arrangement. This arrange- 

 ment has proceeded still further, and disposed distinct masses 

 of the honeycomb limestone to assume determinate forms in the 

 substance of the rock itself. The crystallization of some of 

 these masses appears to have diverged from a centre laterally, 

 until the radii were met by those of other diverging masses, 

 and both became compressed on the sides. The most striking 

 of these forms nearly resembles a papal mitre : they are from 

 six to nine inches in ler.gth or more, and may be detached from 

 the rock. Several of these mitre-shaped masses appear also to 

 have come in contact during their formation, and to be com- 

 pressed at the place of junction, the convexity of theone having 



formed 



