28 An Account of the Great Derbyshire Denudation. 



and ranging in continuity from S.W. to N.E. in certain 

 undulating lines, conformable to the surface, from one sea 

 to the other, just as a certain number at the upper part of 

 the series have been shown to do, by Mr. Smith's manu- 

 script maps. But, after passing the edges of the lias lime- 

 stones and clay strata, in our progress to the westward, 

 from anv of the south-eastern and eastern parts of England, 

 we find on the surface marks of an immense stratum of red 

 earth or marl, which basseting from under the lias clav and 

 sand, seems once to have extended over all the remainder of 

 the British islands, without being now any where covered 

 by patches of upper strata*, much beyond the continuous 

 edge of the lias strata ahovementioned. Instead, however, 

 of seeing the middle and all the western and northern parts 

 of Britain covered by the same red strata, we find now, in 

 this space, numerous local and many very large tracts of 

 strata, surrounded by vertical and connected Jaulls, and 

 greatly lifted and tilted; from the surface of which lifted 

 tracts, the upper red earth, and vast and very unequal thick- 

 nesses of strata, that lay in regular succession below this 

 red earth, have been denudated, " abrupted," or carried off, 

 leaving thus, a great variety of what have been called coal- 

 fields, or mineral-Iiasinsf, in which limited tracts, creat 

 and most important series of strata, are to be seen basseting 

 (owing to the local denudations), of which the basset-edges, 

 or conlmued endings, can no where be traced in these 

 islands, as far as I can learn. Large tracts of the interven- 

 ing spaces, between these denudated mineral basins, are 

 still occupied bv the red marl, containing local strata of 

 gypsum, rock-salt, sand, micaceous grit-stone, &c. &c. in 

 its substance, or exposed by denudation; and in others, 

 local strata, or nodules of great extent, or rather, perhaps, 

 rudely crvsiallized iDasses of slate, green stone, sienite, ba- 

 salt, &c. &c. forming hills or mountains (often intersected 

 by mineral veins) from the tops of which masses, the red 

 marl has in most instances been denudated. It remains a 

 task of great difficultv, yet to be accomplished, to ascertain 

 the lower part of the British series of strata, thus only ex- 

 posed to view, in local and unconnected tracts, or basins, 

 which are in part often concealed by gravel (frequently so, 

 near their borders), and towards which investigation, little 



* Grarels, peat, kc. not being included in this term. 



+ Of which a fine instance is described by Mr. Edward Martin, in the 

 Philosophical Transactions for 1808^, and of which the Forest of Dean pre- 

 sents a smaller, but similar instance. 



5 Called the South Wales Mineral Basin ; and another around Nailsea in 

 Somersetshire, bee p. 323 of our last volume. — Editor. 



has 



