Unconformable Red Marl and Gritstone— Geol. Inferences, 169 



described at page 1 63, undoubtedly has the lower part of the Coal- 

 measures in it, since they appear at Nant-y-Felin Farm, ly m. 

 WSW of Llanganhafal, resting on the Limestone, and in other 

 places I beheve; but these Coal-measures are in most parts con- 

 cealed, by an uncoiformuhle covering of Red- Marl Grit, or by an 

 alluvial covering of Clay and Bolders upon this, in manv places ; 

 and which unconformable and alluvial coverings, in many places 

 concealing the edge of the Limestone also, and causing it to 

 appear in isolated Rocks, have presented the obstacles to the 

 true understanding of the structure of this curious valley, to which 

 I have already alluded in page 1(33. 



If time would permit, I might now adduce alike corroborating 

 instances, from mnnerous other parts of England, of the un- 

 conformableness of that almost universal covering of Red Marl, 

 to all the middle and western parts of South Britain, wliich I 

 mentioned in a paper read to the Royal JSocietv in the spring of 

 1811*. At which time, the unconformable character of the 

 yellow Limestone and sand or grit, below it, was not known, or 

 its relation to the Red Mail understood; and I was likewise un- 

 der the mistake (derived from Mr. Smith) of su])posing the si- 

 tuation of the Somersetshire or upper Coal-measures, (vol. i. 

 pp. 132, 159, 174 and 179 of my Derby. Report,) to be above 

 the yellow Limestone, instead of heloiv it; and instead of con- 

 sidering this last Rock as only occasionally found, among the 

 anomalously imbedded substances of the Red Marl, which I had 

 endeavoured to enumerate in my Derby. Report, i. p. HS. 



The Geological In/hences then, which appear to me deduci- 

 ble from the above, are, that tiie British series of Strata is re- 

 ducible into two very distinct parts, the product perhaps of very 

 distant periods of time; the lowest or first, in which coarse Slate f 

 and numerous other substances imbedded in the same, were de- 

 posited, and left with a very uneven surface ; then Limestone of 

 very variable thickness and separated locally into distinct Rocks, 

 by intervening matters of very diiTerent natures ; then a vast 

 series of Coal-measures, very improperly, I think, called " Inde- 



* See die xxxixtli volume of tlie Phil. Mag. pr.ge 28. 



t Many, 1 am aware, will \,c ready to exclaim that this is brgiiinin;: at 

 llie surface ouly of the crust of the Earth, while their theories enable 

 tiKin to descend to older and still lower liocks, in exact order, to t!:e very 

 centre of ourOlijhe: — he it so, ])rovided they can account for its total 

 spccilic gravity? I will however take the liberty of saying, that their ^cfo- 

 f^iwstic floqmris afford no helps towards usefully exploring and nnder- 

 btanding tin; Uritisli Strata which are accessible, but I'li the contrary, have 

 most materially impeded the knowledge to be obtained, on Smtthiun prin- 

 ciples, of tiie actual structure of our Country, as deep as it concerns tis 

 iiiatorially to knuw it, and from whence important benefits would liow to 

 ■Srieiice, and to the arts and property of the kingdom. 



pendent," 



