S6i Mr. Horner o« ihe Geology of the 



Derbyshire and Staflfordshire, 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 rela- 

 tion, in point of position, to the other secondaiy 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 Watchet, it forms, as I shall presently 

 shew, a very prominent feature in the mineralogy of this part of 

 ihe country. I found it in almost every situation where the deri- 



