STRATA 0? SHROPSHIRE AND DENBIGHSHIRE. 21 



Section 10 is one of Mr. Binney's, given by Mr. Hull*. I insert it 

 because of its resemblance on a restricted scale to that of Ardwick 

 on the one side and that of Ifton on the other. It is separated 

 from the last by a distance of about forty miles ; and the country 

 between consists of a trough filled up with Triassic beds which hold 

 the great salt-deposits of Cheshire. 



Section 11 is that of Ifton, which I have already described, and to 

 which I shall have occasion to refer again. 



Section 12 is one which, in its middle portion, group 3, is well 

 known and often quoted. It was, I think, first described by Prof. 

 Sedgwick f, in the year 1832, though alluded to by Messrs Cony- 

 beare and Phillips in 1822 ; and it has subsequently been noticed 

 by Sir R. I. Murchison, Prof. Ramsay, Mr. E. W. Binney, Mr. Hull, 

 and others. Prof. Sedgwick described it, in descending order, as 

 follows : — 



Group 4. " Red and variegated sandstone descending into the great plain 



of Shropshire, and of unknown thickness." 

 Group 3. "A very fine magnesian conglomerate, in mineral structure like 



the Bristol and Devonshire conglomerates." 

 Group 2. " Coarse reddish sandstones, in character intermediate between a 



coarse coal-grit and a true red or variegated sandstone." Between this 



last and the upper coal-measures may now be added various green 



rocks, breccias, and conglomerates." 

 Group 1. " Coal-measures." 



Sir R. I. Murchison places the conglomerate group 3, on the same 

 horizon as the Ardwick limestone bands and the Magnesian Lime- 

 stone beds of the north-east counties. Mr. Hull, however, is inclined 

 to place it, along with the conglomerates of Shifihal, South Stafford- 

 shire, and Enville, in the lower part of the Permian series. In 

 deciding a point of this kind, the position the strata occupy is of 

 more importance than their mechanical structure and the deriva- 

 tion^: of the materials of which they are composed. Seeing, then, that 



* Geology of the Country around Bolton le Moors, p. 17. 



t Geol. Transactions, ser. 2, vol. iv. p. 398 et seg. 



| A few words concerning the derivation of the limestone fragments and 

 boulders of this conglomerate may not be out of place here. They are derived 

 fragments, and not concretions formed with the rock like those of Coedyrallt. 

 Mr. Hull, in the work quoted below 1 , assigns some of them, as does also Prof. 

 Bamsay, to the Mountain Limestone, and others to the thin band of Sjpirorbis- 

 limestone which, at some depth, lies between them and the coal. In considering 

 this explanation several difficulties meet us : — 1. While in colour the fragments 

 have a general resemblance to the lower cream- and buff-coloured beds of the 

 Mountain Limestone, they are of a paler cast, and often have a greenish tinge. 

 2. There is an entire absence of the gritty, reddish, and greyish beds of the middle 

 portion, and also of the bluish-grey beds of the upper series of the Mountain 

 Limestone of North Wales. 3. Hitherto I have failed to detect in them any 

 Mountain -Limestone fossils. 



Then the Spirorbis -limestone, at the most, consists of only thin bands, and it 

 would take the denudation of a large area to supply the materials for this con- 

 glomerate. It is also closely associated with coal-strata ; and if it supplied the 



1 Triassic and Permian Rocks of the Midland Counties, p. 21. 



