ture with that observable in the mountain-limestone of Crich Hil. in Derbyshire, of which we have already spoken (p. 699). 1. Wenlock shale. LIGN. 3. Coal-measures. 2. Wenlock or Dudley limestone. 14. THE CLENT HILLS.-In the above-described section, the upheaved and contorted. sedimentary deposits are alone displayed; the deep-seated volcanic mass, by which they were elevated and thrown into their present position, being concealed from view. But in several places in the surrounding district, the intrusive igneous rocks appear above the surface, in sharply-defined ridges; as in the Rowley Hill, near Dudley, and those of the Clent, Romsley, and Lickey; and the more distant ranges of Abberley and the Malverns in Worcestershire. About two miles to the south of the Dudley coal-basin, and stretching in a parallel direction with the Silurian range previously described, is another chain of hills, about six miles in length, and varying in height from 800 to 1000 feet, called the Clent Hills.* This elevated district is formed by a protrusion of felspathic trap-rocks through Permian strata, consisting of conglomerate and sandstone, with cornstone and traces of coal, as shown in Lign. 188.+ This basaltic eruption must have taken place after the Carboniferous strata were deposited, and long *Within the precincts of the Clent Hills are Hagly, the seat of Lord Lyttleton, which the muse of Thomson has rendered classic ground, and the equally celebrated Leasowes of Shenstone. The trap or volcanic rock of the Clent, Lickey, and Abberley Hills is chiefly composed of brownish-red compact felspar, occasionally porphyritic, and sometimes passing into a fine concretionary rock.-Sil. Syst p. 496; and Records Geol. Survey, vol. i. part 2, p. 240. antecedent to the Triassic period, the strata of which age have been quietly deposited on the southern flank of the Clent Hills, as seen in Lign. 188. The following description by Mr. Hugh Miller is too characteristic to be omitted : "The New Red Sandstone, out of which the Clent Hills rise, forms a rich, slightly undulating country, reticulated by many a green lane and luxuriant hedge-row; the hills themselves are deeply scooped by hollow dells, furrowed by shaggy ravines, and roughened by confluent eminences; and on the south-western slopes of one of the finest and most variegated of the range, half on the comparatively level red sandstone, half on the steep-sided billowy trap, lie the grounds of Hagly. Let the Edinburgh reader imagine such a trap-hill as that which rises on the north-east between Arthur's Seat and the sea tripled or quadrupled in its extent of base, hollowed by dells and ravines of considerable depth, covered by a soil capable of sustaining the noblest trees, mottled over with votive urns, temples, and obelisks, and traversed by many a winding walk, skilfully designed to lay open every beauty of the place, and he will have no very inadequate idea of the British Tempe sung by Thomson. We find its loveliness compounded of two simple geological elements,— that abrupt and variegated picturesqueness for which the trap-rocks are so famous, and which may be seen so strikingly illustrated in the neighbourhood of Edinburgh, and that soft-lined and level beauty-an exquisite component in landscape when it does not stand too much aloneso characteristic, in many localities, of the Lower New Red Sandstone formation. . . . . . From the hill-top, the far Welsh mountains, though lessened in the distance to a mere azure ripple, that but barely roughened * * The eminence so glowingly described by Thomson :— "Meanwhile you gain the top from whose fair brow ..... the line of the horizon, were as distinctly defined in the clear atmosphere as the green luxuriant leafage in the foreground, which harmonized so exquisitely with their blue. The line extended from far beyond the Shropshire Wrekin, on the right, to far beyond the Worcestershire Malverns, on the left. In the foreground we have the undulating trap. Next succeeds an extended plain of the richly-cultivated New Red Sandstone, which, occupying fully two-thirds of the entire landscape, forms the whole of what a painter would term its middle ground, and a little more. There rises over this plain, in the distance, a ridgy acclivity, much fretted by inequalities, composed of an Old Red Sandstone formation coherent enough to have resisted those denuding agencies by which the softer deposits have been worn down; while the distant sea of blue hills, that seem as if toppling over it, has been scooped out of the Silurian formations, Upper and Lower, and demonstrates in its commanding altitude and bold wavy outline the still greater solidity of the materials which compose it."* and 15. THE WREKIN.-The Dudley coal-field is remarkable for the beds of volcanic grit intercalated between the upper strata of the Coal-measures and the Permian deposits; which Sir R. Murchison is of opinion were formed from the detritus of submarine volcanos, which were in activity towards the close of the Carboniferous epoch.† The solid intrusive trap-rocks are of a later date, and appear in various detached points near Dudley. The largest mass constitutes Rowley Hill, a ridge two miles and a half long, and one mile wide, extending from Rowley Regis to the southern suburbs of Dudley. This trap-rock, known locally as the Rowley-rag, is a hard, fine-grained, crystalline green-stone, or basalt, being an admixture of grains of hornblende with small crystals of felspar and quartz. This mineral appears in a slender columnar form in Pearl Quarry, near Timmin's Hill, at Rowley. * "First Impressions of England and its People," by Hugh Miller; London, 1847, p. 111, &c. + "Silurian System," p. 468. This trap-rock supplied the materials for the important experiments, by Gregory Watt and Sir James Hall, on the fusion and cooling of rocks; and has of late been employed by Messrs. Chance, at Oldbury, near Birmingham, in the manufacture of molten indestructible architectural materials. 728 feet. The Wrekin 1320 feet. Little Wenlock. Hatch-bank. 1 N.W. Fault. S.E. 6. Wenlock shale. 1, 1, 1. Trap-rock. 2, 2. Quartz-rock: Lower Silurian strata altered from contact with the trap. 3. Caradoc sandstone. 4. Carboniferous limestone. 5, 5. Coal-measures. LIGN. 189.-SECTION THROUGH THE WREKIN TO THE VALLEY OF THE SEVERN. (Sil. System, p. 225, pl. 29, part of fig. 17.) But one of the most remarkable examples of erupted trap in this part of England is that which has formed the hill called the Wrekin, near Wellington in Shropshire, on the north-west flank of the coalfield of Coalbrook Dale; and which must have taken place after the accumulation of the Silurian strata, as the latter were evidently thrown into inclined positions before the Carboniferous were deposited.* At a subsequent period, and long after this consolidation, the coal-measures were in their turn pierced and traversed by other intruded masses of igneous rock, differing in mineral matter, but erupted in contiguous lines of fissure, parallel to that of the Wrekin. The Wrekin is an elliptical hill, about a mile and a quarter long, its highest summit being 1320 feet above the level of the sea. It is composed of igneous rocks, having on its flanks various members of the Silurian and Carboniferous systems, as shown in the section, Lign. 189. The sedimentary deposits within the influence of the erupted volcanic rocks have undergone considerable alteration; the sandstone being changed into granular quartzrock, much of which is pure white quartz, with particles of decomposed felspar, and sometimes much resembling submarine volcanic dejections: in some places this rock becomes a brecciated aggregate. The igneous rock-masses are various modifications of pink and deep * The erupted trap forming Barrow Hill (see p. 700) is another instructive example of this phenomenon. red syenite, consisting of compact felspar with white quartz, and disseminated chlorite: in some parts the mass is made up of felspar with green-earth and veins of carbonate of lime. To the south-east of the Wrekin, bosses of a basaltic green-stone, of irregular shape, appear around the village of Little Wenlock (Lign. 189). Herefordshire. Mathon. W. 8. New Red Sandstone. fig. 7.) 3. 3. Wenlock limestone. 4. May Hill sandstone and grit, overturned. (Sil. Syst. pl. 36, זי The invaluable work to which I am indebted for most of the interesting facts thus briefly noticed should be referred to for full details of the geological structure and relations of the deposits under review. The eminent author considers that this district of Shropshire affords unequivocal evidence of the alternate activity and repose of volcanic action, during very long periods in the palæozoic ages; and that the following sequence of geological events is clearly established:-1. that volcanic grits were formed during the deposition of the Lower Silurian strata ;-2. the Upper Silurian rocks and Devonian sandstone were accumulated tranquilly, without a trace of contemporaneous eruptions; 3. after their consolidation, the last-mentioned deposits were dismembered, and set upon their edges by vast outbursts of intrusive trap ;-4. the Carboniferous beds were deposited after the older strata were upheaved; and 5. that subsequent dislocations, including some of the most violent with which we are acquainted, took place after the deposition of the Coalmeasures and Permian sandstone.* 16. THE MALVERN HILLS, &c.— In Worcestershire, the different members of the Silurian system are well developed, and, though occupying a narrower zone than in Shropshire, constitute a continuous band for a distance of between twenty and thirty "Silurian System," p. 235. This subject is also treated of in "Siluria." |