412 



the author shows is nothing more than altered Caradoc sandstone, 

 precisely analogous to that which he has on former occasions pointed 

 out on the flanks of Caer Caradoc, the Wrekin, Stiper stones, &c. In 

 those districts the passage from a fossiliferous sandstone to a pure 

 quartz rock has been accounted for by the latter being in absolute 

 contact with eruptive masses of igneous origin; and here it is sug- 

 gested that the same cause may have operated, though the contact is 

 not visible, because the line of quartz rock is precisely upon the pro- 

 longation of the trappean axis of the Rowley Hills, whilst the southern 

 end of the parallel outburst of the Clent Hills, is but little distant. 

 Notwithstanding their highly altered condition, it is shown that all 

 the quartz rocks throughout this ridge of low hills are uniformly stra- 

 tified, the dip being cither to the E.N.E. or W.S.W., i. e. at right 

 angles to the direction ; and the parallelopipedal fragments into which 

 the rock breaks are shown to be produced by fissures more or less at 

 right angles to the planes of stratification ; these fissures being so 

 numerous where the mass is much altered, as almost to obscure the 

 true laminae of deposit. 



4. 2rap. — The composition and characters of the trap rocks and 

 basaltic masses of the Rowley Hills are first described, together with 

 the manner in which they are supposed to rise through and cut off 

 the coal upon their flanks. Rocks of similar origin occur at various 

 detached points to the west of Dudley, of which Barrow Hill is the 

 principal, affording the most convincing proofs of the volcanic mass 

 having burst through the carboniferous strata, since the latter are not 

 only highly disturbed and broken, but fragments of coal and coal mea- 

 sures, in highly-altered conditions, are found twisted up upon the sides, 

 and even mixed with the trap itself. In the Wolverhampton or north- 

 ern coal-field, the chief vent of eruption is at Pouk Hill, two miles west 

 of Walsall, where the greenstone is arranged in fan-shaped columns. 

 After pointing out distinct evidences of the intrusion of similar rocks 

 at Bentley Forge and the Birch Hills, in some of the old open works 

 near which the trap is seen to overlie the coal, the author gives vari- 

 ous sections of subterranean works, which prove the existence of 

 greenstone, in bands more or less horizontal. As these bands of trap 

 have jagged edges, are of limited extent, of exceeding irregularity 

 in thickness, and often produce great alteration upon the inclosing 

 carbonaceous masses, the author has no hesitation in expressing his 

 belief that they are not true beds, but simply wedges of injected matter 

 which have issued from central foci, and have been intruded laterally 

 amid the coal strata; an opinion formerly expressed by Mr. A. Aikin 

 in an able memoir*. 



Although these lateral masses of greenstone in the Wolverhampton 

 field are of origin posterior to the accumulation of coal strata, the 

 author does not deny that the tufaceous conglomerates of Hales Owen, 

 which have a strong analogy in composition to a certain class of vol- 

 canic grits described in former memoirs, may have been formed con- 

 temporaneously with the carboniferous deposits. 



The trap of the Clent Hills is then briefly described, and is shown 



* Transactions Geo). Soc, 1st Series, vol. iii. p. 251. 



