NILS HILL.— ORGANIC REMAINS. — STRIKE AND JOINTS OF QUARTZ ROCK. 285 



genus 1 . Another form, still more resembling an organized body, which I detected in my last visit, 

 is probably an orthoceratite. 



Small flakes of anthracite occur, though rarely, in cavities and joints. The same rocks continue 

 from Nils Hill to the village of Pontesbury, near which their north-western face is covered by a 

 "breccia in place" of angular lumps of the quartz rock, forming thick beds, which hanging upon 

 the side of the hill constitute the fringe of the adjacent coal-field, towards which they dip at a 

 slight angle, thus presenting a strong contrast to the highly inclined parent rocks on which they 

 rest 2 . 



The quartz rock of Nils Hill is so well exposed in quarries, that we acquire a much more 

 precise knowledge of its structure than in the weathered and dismantled bosses of the Stiper 

 Stones. We here see that on the opposite sides of the transverse combs the directions of the strata 

 of quartz rock diverge in their direction and have different degrees of inclination. On the north- 

 north-eastern side of the comb in which the great quarry is situated, the chief mass trends from 15° 

 and 20° west of south to 15° and 20° east of north, and dips 60° to 70°; whilst on the south- south- 

 western side the same beds striking north and south are vertical, and even in part thrown over beyond 

 verticality. The nature of those transverse fractures which have broken up the ridge of the Stiper 

 Stones into a number of disjointed and separate ledges is thus explained ; for we perceive that it 

 would have been impracticable to tilt these once continuous strata into the divergent directions in 

 which they are now placed without producing transverse ruptures or faults. So vibratory and 

 oscillating, indeed, have been the movements by which the strike of the masses has been determined, 

 that even in the same ledge we meet with differences of direction, amounting to 30° and 35°, in beds 

 only fifty to eighty feet from each other in the order of superposition. 



Nils Hill is further an excellent spot to observe the numerous joints into which the quartz rock 

 is divided, and which have been alluded to as obscuring the true lines of deposit in the Stiper 

 Stones. The prevalent joints form backs, i. e. their planes are at obtuse or right angles to the sur- 

 faces of the beds. Most of the joints trend diagonally to the strike, so that the true dip of the strata 

 lies in a direction between these diagonals, as in many cases previously alluded to. (See jointed 

 structure of Upper Silurian Rocks, chapter 20.) There are, however, examples of other joints which 

 mark the true lines of strike and dip. Referring to the Appendix for other observations on joints, 

 it is sufficient to state that at this spot they have given relations to the strata, and that their direction 

 changes with every variation in the strike of the mass. 



The rock of the Stiper Stones passes upwards into sandstone, which in its turn dips 

 under the schists forming the mining ground of Snailbatch and Penally, &c. These 

 transitions in the ascending order are exposed on the sides of the deep and picturesque 

 ravines of Mytton's Dingle 3 , the Crow's Nest, &c. 



The conversion of sandstone into quartz rock having been shown to take place in 

 several points where such strata are in contact with rocks of igneous origin both in this 

 district and other parts of Salop, there can be no doubt that the structure of the Stiper 



1 Tn perusing a MS. of Mr. Arthur Aikin, I perceive that he also observed what he considered to be 

 fossils in this quartz rock near Pontesbury. 



2 A similar breccia recomposed in situ occurs on the summit and sides of the Lickey quartz rock. 



3 Vulgarly called Mutton Dingle. 



2 N 



