Border Country of Salop and North Wales; ^c. 247 



of the rock. Where this rock is quarried^ the recent opening's are commonly 

 marked by its great conchoidal fracture ; and the same principle of aggre- 

 gation which produces this kind of fracture^ produces also the forms of the 

 concentric lamellar concretions elicited under the influence of slow decompo- 

 sition. 



Immediately above Downton Castle, Mochtre Hill rises to the N., its strata 

 dipping towards the river Tame. Along its ridge are quarries of limestone : 

 in one of them, called Weaver's Quarry, the upper strata are thin beds of 

 shale with calciferous sandstone in nodular masses, forming irregular strata 

 between the beds of shale : the limestone lies conformably to the beds above 

 it in strata of very considerable thickness. 



The most curious and one of the most frequent fossils of this vicinity is the 

 Pentamerus Knightii, (figured in Sowerby's Mineral Conchology, PI. 28.) 

 a different species of the same extraordinary shell, which has been noticed in 

 the quarries at Norbury. The shell consists of fibres perpendicular to the 

 plane of the substance which they compose. The septum, which divides the 

 shell longitudinally into two parts, has a natural parting down the middle. Its 

 two portions are contiguous below, but divide above so as to inclose a small 

 longitudinal cavity. The connection of the septum with the external curva- 

 ture of the shell is very remarkable. The fibres of the septum being per- 

 pendicular to its plane, meet at right angles the fibres of the curved exterior 

 portion. They do not intermix, but terminate upon a plane, which bisects 

 the right angle formed where the septum meets the exterior curvature both 

 above and below. The shells have a tendency to separate both in the direc- 

 tion of these small planes, and of the broader plane, which divides the septum 

 into its two parts. The fibrous structure, which has now been described, 

 resembles that in the bone of the cuttle-fish, the fossil mytilus, &c. 



4. A fourth district, respecting which I shall now notice some particulars, 

 is the country in the vicinity of Church Stretton. The "transition, or newest 

 primitive clay-slate," as it is denominated by Mr. A. Aikin, constitutes the 

 mass of the Long Mountain, which fills up the greater part of the space be- 

 tween the line of section just traced, and the region on which we now enter: 

 it shows itself on the western border of the town of Church Stretton ; it is 

 here highly inclined, and much contorted ; its beds are thin, passing into a 

 soft shale ; but it includes beds of a harder and coarser schist, and in all its 

 general characters corresponds with the appearances of the country about 

 Llansilin and other places already described. In contemplating the hills on 

 the other side of the town and of the Watling Street, which passes by its 



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