352 Mr. Horner on the Geology of the 



§ 15. In the quarries at Great Hoi well there may be seen on a 

 small scale that occurrence of caverns so frequent in limestone. 

 They vary in width from half a foot to five feet, and their height 

 varies with the thickness of the beds. In some places they may be 

 seen to close, but in general their depth was beyond what I could 

 ascertain. Their sides although uneven by the irregular projections 

 of the rock have all a smooth rounded surface, as if worn by attri- 

 tion, but this seems to be owing to an incrustation of calcareous 

 spar which hangs down in many places in large stalactites, a process 

 that is evidently going on at the present time in several of these 

 caverns. That the caverns have not been produced by any rents 

 that might have occurred after the consolidation of the strata, is 

 evident from their being confined to the limestone and not extending 

 through the intervening slate. 



§ 16. Nests of copper are very frequently found in this lime- 

 stone. I observed in several places small nodules of the green 

 carbonate enveloped by brown ochreous earth. At Doddington a 

 very large quantity was found some years ago. A loose friable 

 quartzose sandstone, which I shall afterwards notice, was found to 

 contain so much copper ore that a mine was sunk in it. In order to 

 drain the works which were situated upon the rise of the hill, a shaft 

 was sunk for the purpose of driving a level from north to south up to 

 the workings, expecting at the same time to cut across any veins of 

 metal that might exist there, as they are generally supposed in this 

 part of the country to run east and west. They had proceeded a 

 very short way in driving this level when they came upon a black 

 slaty limestone, and immediately afterwards they found a large nest 

 of copper ore, consisting of the green carbonate, and yellow sulphuret. 

 The workings in the sandstone were immediately given up ; they 



