As I happened to be at a gentleman’s house near Edinburgh, in whose estate there was a great deal of coal, and who was at that time working a level or adit, in order to drain off the water, I observed, that the current of water, which flowed from this level, separated a great quantity of ochre, and, emptying itself into a river soon after it came from the entry of the level, tinged all the stones and the channel of the river, for a good way, of an ochrous colour. The taste of this water was exactly like that of a common steel Spaw; and it afforded a purple colour with galls[55]. As I knew, that this water flowed off a great body of coal, I often infused that fossil, taken from the pits near this level, in common water; but the infusions never yielded any tincture with galls. I tried in the same way another mineral, that the miners call _blaes_; which is a cliffery stratum of a blueish colour, that often lies both above and below the coal: also another fossil of a brown colour, which is very ponderous, and is called by the miners _dogger_; a thin seam of which often lies in the midst of the coal. However, neither of these would afford an infusion, that would tinge with galls. At last I got another mineral out of these coal-pits, which is sometimes found amongst the coal, but is not so frequent as any of the former; and this fully answered my expectation. It is found either in round or broad pieces, is exceeding ponderous, and of a shining yellow colour, and is called by the miners _brass lumps_. When I infused this mineral for a short time in common water, it communicated to it all the properties of a steel Spaw; its taste was exactly the same; and it received a tincture from galls, which was of a more diluted or intense purple, according to the proportion of the mineral added to the water, or to the time of the infusion. This simple experiment does therefore clearly discover to us the origin of steel waters, and the manner, in which they are impregnated with their mineral contents in the bowels of the earth. This observation, which I had made concerning the origin of steel waters, led me, when I first visited Hartfell-Spaw, to inquire into the adjacent fossils: which was the more easily done, as the strata of the earth about the well, for a considerable depth, are exposed to view. After some search among these, I found a stratum of cliffery rock, about three or four feet thick, of a grey colour, and, I think, about twenty paces from the spring. In some of the hollow places of this rock, where the rain and wind did not reach, I observed a white saline efflorescence on its surface, which when I had taken off and tasted, I concluded, from its styptic and chalybeat taste, that it was a native vitriolum Martis, notwithstanding its white colour; but I found it, upon trial, to be alum, having some fine attenuated parts of iron conjoined with it, and the same salt with that contained in the Spaw water.