Derbyshire and Staffordshire, the salt mines of Cheshire, and the brine springs at Droitwich in Worcestershire, and which is known by the name of red marl, red ground, &c. There are few rocks which present a greater variety of forms of aggregation, and about which there are so many contradictory opinions respecting its relation, in point of position, to the other secondary strata that lie contiguous to it. To investigate the mineralogical and geological history of this rock would be a most useful inquiry, and not merely as a matter of science, but in an economical point of view, from its intimate connection with the coal formations. There is undoubtedly in the district I am now describing an appearance of this rock having a common origin with the other varieties of the derivative rocks, as a series could without difficulty be collected, shewing an insensible gradation from the one to the other, and the patches of greenish sandy clay I have mentioned in the conglomerates § § 24, 26, are another strong point of resemblance. It never has been ascertained, I believe, what is the chemical difference between these greenish grey patches, and the red rock into which they seem to graduate. In many other places this red marly sandstone is accompanied by similar conglomerates, and I observed in the collection of my friend, G. B. Greenough, Esq. a specimen from Alderley Edge, in Cheshire, identical with that variety of conglomerate found at Alcombe, § 23, which contains sulphate of barytes, and carbonate of copper.─Although I found it always above the conglomerates in this district, I am informed by Mr. Greenough, that this is by no means a general rule. In that part of the district which I have already described it occurs to a very limited extent in point of thickness, but on the sea shore in the neighbourhood of Watcher, it forms, as I shall presently shew, a very prominent feature in the mineralogy of this part of the country. I found it in almost every situation where the derivative
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