Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/360



§ 15. In the quarries at Great Holwell 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 attrition, 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 limestone. 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 blast 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