miles; viz. from the northern end of the Abberley Hills, to the southern extremity of the Malverns; "and, though the strata are dislocated, and even through a course of four miles entirely reversed, yet they maintain a prevalent inclination to the west, and dip beneath the Old Red Sandstone of Herefordshire. Emerging through the Silurian deposits, and forming a buttress on their eastern flank, are certain igneous rocks, which, in the Abberley Hills, protrude only at intervals through the dislocated strata, but in the Malverns constitute a narrow ridge of syenite, rising to some height above the Silurian deposits; "* as represented in Ligns. 190, 191.

The Malvern Hills are situated in the south-western part of Worcestershire, and consist of an uninterrupted chain about nine miles long, and two wide, the highest summits attaining an altitude of nearly 1500 feet. This outline,

1. Altered Lower Silurian sandstones and schists. 2. Black schists with Olenus 3. May Hill or Upper Llandovery sandstones and conglomerates. 4. Woolhope limestone. 5. Wenlock shales and limestone.

when viewed from a distance, as, for example, from the heights above Cheltenham, is very striking, and characteristic of their geological structure. The three highest points are the Herefordshire and Worcestershire beacons, and North

*"Silurian System," p. 410; "Siluria," p. 92; and Phillips' Memoir on the Malvern and Abberly Hills, in the Mem. Geol. Survey, vol. ii. part 1; also his "Manual of Geology," p. 513; and Notices Roy. Instit. Great Brit. 1857, part 7, p. 386.

+ See also "Siluria," p. 94; ibid., 2nd edit. p. 192, &c.

Hill (Lign. 190), formed by the protruded syenitic rocks, which form the nucleus of this mountain-range.*

In passing from Herefordshire to Worcestershire, in a line from west to east (see Lign. 190), the Devonian or Old Red strata first appear, and are succeeded by the Upper Silurian, namely, the Ludlow and Wenlock deposits; next follow beds of May Hill sandstone, and we then arrive at the protruded peaks of igneous rock, and descend over the Permian Conglomerate and Triassic strata to the plains of Worcestershire. The relative position of the strata and the erupted rocks is shown in the anexed diagrams (Ligns. 189, 190, and 191). The entire succession of the Silurian series, between the Syenite of the Malverns and the Old Red Sandstone, is well exposed in a transverse section from Midsummer Hill to Ledbury.

There is one feature in the geology of the Malvern Hills that demands particular notice. The Silurian strata in immediate contact with the syenite are sometimes partly bent back, or inverted, as shown in the section, Lign. 190, in which the Wenlock limestone (3.) is seen at a distance from the syenite and unaffected, whilst the May Hill sandstone and grit (4.) are overturned and dip in an opposite direction.

In the Abberley Hills, the same phenomenon appears in a more striking point of view; and through a range of four or five miles, the Devonian, Ludlow, and Wenlock strata are completely inverted, the newer formations being overlaid by the older; "so symmetrical, indeed, is the reversal in this part of the range, that any geologist who had not previously made himself acquainted with the true order of superposition would naturally conceive the Wenlock limestone to be younger than the Ludlow rock, and the Ludlow rock than the Old Red Sandstone." †

The Lickey Hills, which are situated about three miles from the southern extremity of the Dudley coal-field, consist of a narrow ridge of quartz-rocks, about three miles in length and four or five hundred feet high, and are referred by Sir R. I. Murchison to the Upper Llandovery

* A very interesting Memoir on the mineralogy of the Malvern Hills, by Mr. Leonard Horner, was published in the Geol. Trans. 1st ser. vol. i p. 281.

"Silurian System," p. 421.

sandstone; the quartz-rock of the Lickey gradually passing into a fossiliferous sandstone containing the characteristic organic remains of the Pentamerus-zone." A mass of trap, being the prolongation of that of the Clent and Abberley Hills, forms the nucleus of the ridge, and appears in the point called Lickey Beacon, on the northern end of the Bromsgrove Lickey Hills, which consist, in great part, of Permian and Triassic strata.†

The Valley of Woolhope, which lies to the west of the southern extremity of the Malverns, about three or four miles from Hereford, is a remarkable instance of what geologists term a " valley of elevation;" being a dome-shaped protrusion of Silurian rocks through the Devonian deposits, of which the surrounding region consists. This elevated mass of strata is of an oval form, being six miles long, and four wide. Within this area, the Upper Silurian strata are thrown up into concentric and conformable masses, each dipping outwards from a common centre, and the whole passing beneath the Old Red Sandstone. The central nucleus consists of quartzose grits belonging to the Mayhill sandstone or Upper Llandovery group. The trenches surrounding the central mass have been produced by the degradation of the more perishable beds, and the denudation of the harder rocks.

I must not conclude this brief sketch of the geological phenomena of the British Silurian series, without referring to the evidences of submarine and possibly sub-aerial volcanos having existed in Silurian times. During the period when the Llandeilo flags and their equivalents were accumulated over the area extending from the Malverns to Pembrokeshire, volcanic vents existed, whence molten matter and ashes were ejected, and became intermingled with the detrital accumulations of the period. The volcanic ashes were mixed up with the gravels and sands that are now in the state of conglomerates and sandstones, and accumulated in beds that are interstratified with the mud and sand. These igneous products were erupted prior to the granites of those districts.

The great peaked mountain-masses of Snowdon and Cader Idris, in Wales, are formed of Lower Silurian strata interstratified with contemporaneous volcanic grits, and traversed by subsequent dykes and pro

See "Siluria." The quartz-pebbles so largely distributed over this part of England, and extending into the valley of the Thames, are waterworn fragments of the rocks composing this ridge; see p. 220.

+ "Silurian System," p. 493.

66

Ibid. chap. xxii. p. 488.

§ 'Silurian System," chap. xxii. and xxvi. &c.; and Mem. Geol.

Surv. vol. i. pp. 33 and 35

trusive masses of igneous rocks. The strata of Cader Idris are Lingulaflags; those of Snowdon are Caradoc sandstone. Of the igneous rocks of the Upper Silurian period some notice has already been made at page 813.

In the Devonian strata also, near Tavistock and in South Devon, vol canic ash is intermingled with the argillaceous slates and limestones.*

17. SILURIAN AND CAMBRIAN STRATA OF EUROPE AND AMERICA. Since the publication of the "Silurian System," much has been done to determine the position of the foreign sedimentary deposits formerly known to geologists by the general term of Transition-rocks; and, so far as recent observations have ascertained the characters and relations of the most ancient fossiliferous strata on the Continent, they are all referable to the same geological period as the Silurian and Cambrian formations of England.

In France † the oldest palæozoic rocks are Lower Silurian, which are succeeded by the Lower Devonian; the Upper Silurian being absent. In Bohemia, especially around Prague, both Lower and Upper Silurian strata, often extremely rich in fossils, are largely developed; and have been admirably elucidated by M. Barrande.‡

Throughout Scandinavia § crystalline rocks occupy the surface of the country to a vast extent, and are covered in many places by sedimentary strata containing Silurian fossils. Near Christiania in Norway, the Lower Silurian deposits occupy a long trough in the gneissic rocks; and the little islands in the Bay contain Upper and Lower Silurian strata; the

* Mem. Geol. Survey Great Britain, vol. i. pp. 83 and 90. + Siluria," p. 383.

"Système Silurien de la Bohème." Besides this noble result of his labours, in the form of the first volume (4to) of a magnificently illustrated and comprehensive work on the rocks and fossils of the Silurian basin of Bohemia, M. Barrande has published numerous papers and memoirs in the geological publications of Paris and Germany. A complete epitome of his views, ably drawn up by his friend, Sir R. Murchison, may be consulted in "Siluria." See also a full notice of M. Barrande's great work in the Annals of Nat. Hist. 2nd ser. vol. xii. p. 130.

§ See "Geology of Russia," &c. p. 10, &c.

entire series, with a multitude of typical fossils, being exhibited in very small areas.

*

The Isle of Gothland exhibits a fine series of Upper and Lower Silurian rocks. Throughout a large part of the province of Scaraborg, in the south of Sweden, the Silurian strata are perfectly horizontal; the different subordinate formations of sandstone, shale, and limestone occurring at corresponding heights in hills many leagues distant from each other, with the same mineral characters and organic remains. It is clear that they have never been disturbed since the time of their deposition, except by such gradual movements as those by which large areas in Sweden and Greenland are now slowly and insensibly rising above, or sinking below, their former level.

In Russia and the Baltic Provinces + the lower division of the Silurian system is characterized, as elsewhere, by the abundance of Orthides, Leptænæ, and other brachiopodous shells, Orthoceratites, and Trilobites; the middle, by Pentameri; and the upper, by large masses of corals, especially of Favesites, Catenipora, &c. ; and the Devonian strata teem with remains of the typical species of fishes, and with Spiriferi, Leptænæ, &c. Throughout the immense extent of Central Russia, forming nearly one-half of the European continent, there are no intrusions of igneous rocks; and the whole of the deposits, from the lowermost to the uppermost, are but little altered, and in many instances are unsolidified; yet each group contains the same typically characteristic organic remains as in England. But in the Ural Mountains and Siberia, the formations of the same age are thrown up into mural masses, broken into fragments, impregnated with metalliferous matter, and exhibiting every variety of metamorphic action. Yet a clear distinction may nevertheless be drawn between these pseudo-igneous masses and the true ancient crystalline rocks on which the Silurian strata of Scandinavia rest. §

In North America a similar succession prevails; and we have thus proof that the modification, extinction, and renewal of species are not wholly attributable either to the alteration in the course of currents, or to the elevations or depressions of the ocean-bed, or to other more or less local causes, but depend on some general laws which govern the entire animal kingdom. It is, too, most remarkable, that in Russia, where the de

* See Sir R. I. Murchison's Memoir on the Geology of Sweden, in Geological Society's Journal, vol. iii. p. 1; "Siluria," p. 316, &c.

+ "Geology of Russia in Europe and the Ural; " and "Siluria.” Quart. Journ. Geol. Soc. vol. xiv. p. 36, &c.

§"Siluria," p. 437.