satisfaction to be authorized to add, that Mr Murchison most fully agrees in our opinion upon this subject.

The value of Mr Lewis's knowledge was attested during the spring of 1832, by his discovering in the black limestone of Sedgeley, near Dudley, a portion of his own Pentamerus limestone,' with its appropriate fossil; the importance of which identification is dwelt upon in the work before us.* And the order of the beds at Aymestry was soon found by the author of this volume to furnish a clue to the true relations of the detached strata in several other disturbed portions of the Silurian rocks, which are found within the outcrop of the old red sandstone, at some miles' distance, and in combinations so perplexing, that without such a guide their order could not be determined.

The first result of Mr Murchison's own enquiries was made public at the original meeting of the British Association, held at York in September 1831, where he exhibited coloured maps, representing the 'transition rocks,' the old red sandstone, and the carboniferous limestone, on the border of Wales.

The 'geological' proceedings of 1832, contain the abstract of a paper on the secondary formations in the neighbourhood of Ludlow, by Mr Wright of the Ordnance Survey; which is the earliest notice that we have seen in print of the upper transition rocks in that quarter. This paper, we have reason to believe, had great topographic merit; but the abstract, however, does not describe any connected series of strata, and does not distinguish the beds by their fossils.

The author's address to the Geological Society, on relinquishing the Chair in February 1833, adverts to the previous elaborate enquiries of Professor Sedgwick on the ancient rocks, and to his own labours during the two preceding summers; and expresses particular obligation to the officers of the Ordnance Survey for their extraordinary assistance; inasmuch as a considerable space within his field of observation had not then been laid down for publication.† It is unnecessary to enlarge upon the value of the maps produced by this Survey to the geologist in the field, as suggesting enquiry, and enabling him to combine the result of distant observations, which, without such assistance, no labour can connect. But here we must acknowledge, that on first seeing the beautiful sheets which represent the tract between Aymestry,

* P. 480, text; and note, p. 482.

†The Aymestry sheet of this map was published in February 1832; that including Wenlock Edge, not until January 1833; the Caermarthen and Hereford sheets, 1831; Brecon, 1832; Merthyr and Cardiff, 1833.

*

Ludlow, and Shrewsbury, almost with the relief and distinctness of a model, and afterwards perceiving, in the country itself, how exactly they express the natural features-the indication of successive outcrops, conformable to those of the midland counties and the east of England, appeared to us so striking, as almost to force the true inferences upon the attention of the geologist; and we felt surprize that a structure, now so apparent, should have so long remained unknown. But a very little reflection was sufficient to correct this error. The fact, that the structure and succession were unknown, is undeniable: and notwithstanding the merit of some of those who preceded Mr Murchison, the region might probably have remained undescribed for an uncertain period, but for the fortunate circumstances which led him to perceive and to demonstrate its geological importance.

The first paper of the author on this region, read before the Geological Society in March 1833, contains some inaccuracies, which are important from their relating to the natural order of the groups in question, and to a point of some interest in the history of the subject. It is stated in the abstract given in the 'Proceedings,' that the fossils of the Wenlock Edge and Dud'ley limestones are nearly the same;' and that the exact position, therefore, which the latter occupies in the Geological " Series of England, is thus for the first time determined;' that throughout its course, in the district included between the Onny and the Lug, this limestone is chiefly characterized by the • abundance of one species of Pentamerus; and, at Aymestry, it is rich in that and other fossils;'-Mr Lewis's name being apparently connected with these statements in a note. It is obvious that the two characteristic limestones of the district are here confounded. Mr Lewis, who did not participate in this mistake, immediately pointed it out; † and it will not escape the notice of our readers, that the Wenlock and Dudley ranges of limestone had been identified in Mr Greenough's maps several years before

* Those who have had an opportunity of examining the exquisite topographical drawings of Mr Carrington, now principal draughtsman to the Survey at the Tower-or of comparing his drawing from the model of the country near Ormes' Head with the original, or with the engraving from it by Bates's method will feel that this is no exaggerated praise. The later portions of the Ordnance Map, besides their fidelity and expressive power, have the great advantage of speaking the same language throughout; the shading being so graduated as to render each sheet a portion of one consistent whole; in which the inequalities of the surface will be represented according to a connected and proportionate system, in the most distant places.

† Geol. Soc. Proceedings,' vol. i. p.

465.

either of these gentlemen had begun their examination of this country.

Thus rectified and augmented by the further observations of the summer of 1833, Mr Murchison was enabled to produce (in January 1834) a tabular arrangement of all the transition groups between the old red sandstone and the ancient slates of Wales, which differs but little from that of the present volume, and was the first distinct announcement of the system on which the book is founded: the groups afterwards called Silurian appearing there, for the first time, in their true order, under the general name of the upper grauwacke series.'

When his views were nearly matured, Mr Murchison gave to the whole series of strata the name of the Silurian System,' and announced that title, in a communication to the Annals of Philosophy' for July 1835, where also the names and subdivisions of the present work are stated.*

From the appearance of the table last mentioned, until the publication of the work now before us, (1839,) no session of the Geological Society passed over without the production of one or more papers in connexion with this subject; and this presentation of the author's labours, in successive portions, appears to us to illustrate remarkably the usefulness of such institutions. Each summer's work was thus wrought into a producible form ; the maps and sections were arranged, and specimens examined; and the whole then submitted to the criticism of the evening meetings of the Society; which-though they must have been of a very general character, since few of the members were qualified at that time to enter into detail-could not fail to suggest many improvements and corrections. The abstracts of the papers thus brought forward in detachments, demonstrate also the author's advance in geological knowledge during the course of his enquiries. New objects continually opened upon him; but, undismayed by difficulty, he did not cease from his exertions till the plan which he had successively extended and

*The term system, which may be considered as a substitute for the German term formation,' has, we believe, been objected to, as indicating something more definite than any assemblage of strata can be asserted to be, especially where examined only in one country; and we shall find that the limit (if there be any boundary) between the Silurian and Cambrian systems, is very indistinct. Group' or 'Series' might perhaps have been preferable words; but it is difficult to find good names for the divisions of strata; and the arrangement of the English series in systems' in the author's reduced map, from which the sketch above given, (p. 2,) has been taken, is not inconvenient.

improved was executed in all its parts. It is only by having witnessed the progress of these labours, or by tracing them in the Proceedings of the Geological Society, and other Journals, that a just impression can be obtained on this subject. If the young student of geology wishes to find an example of the effect of diligence and perseverance, as ensuring ultimate success, he cannot do better than to follow the history of the Silurian System in the pages we have just referred to.

The present volume was published by subscription in 1839, at the request of a great number of resident gentlemen and inhabitants of the country described, and has been brought out with considerable splendour-the illustrations being numerous and excellent. It is divided into two parts: the first, which gives the physical and geological description of the surface and strata, being the work of Mr Murchison himself. The second part, containing an account of the fossils obtained from the several groups, is principally written by the naturalists to whose examination the specimens had been submitted.

The First part contains a description not merely of the Silurian region, but of all the groups, from the lower oolite down to the old red sandstone; and there is not any work, to which we can refer our readers with more confidence, on this important portion of the English series of strata. After an introductory chapter, to the defect of which we have already adverted, the author proceeds in a descending order, through the groups beneath the oolitic series ;-beginning with the inferior oolite in chapters 1 and 2. Chapters 3 and 4, "on the new red system," are excellently worked out; and with a joint paper by the author and Mr Strickland, more recently published,* contain a mass of information, indispensable to a correct acquaintance with this formation in England; and to the distinction of certain portions of it, from part of the old red system, which had previously baffled some of the best observers.

We cannot pass this group without calling the attention of our readers to some anticipations of William Smith, in 1815; which are very creditable to his sagacity. The mass of strata ' usually called coal-measures, is known to be deprived of much ' of the superficial space which it would occupy, by the overlapping of the "red earth." When the unconformability of the 'red earth shall be more generally known, and its irregular thickness more correctly proved, it is highly probable that much more coal may be discovered; and the coal-measures be found as regu

* Geol. Trans., 2d series, vol. v. pp. 331, 348.

6

larly connected as other strata. This opinion is confirmed, by 'the great obscurity of coal-measure outcrops in many of the 'districts where coals are now working; and it may be further remarked, that those coal districts, which are near to, or sur'rounded by red, show less of the superficial character common to those strata, than any other parts of their extensive course.

,崇

Mr Murchison has mentioned several cases in which valuable coal has been discovered, in situations where its existence was at one time quite unsuspected, by sinking to great depths through incumbent masses of the new red sandstone; and has strongly urged the expediency of continuing such researches.

Chapter 5, compares the ancient trappean rocks with the products of existing volcanoes, with a view to the illustration of the intrusive masses traversing the new red and carboniferous series. The phenomena of Graham Island and other recent volcanic ejections in the Mediterranean, are employed to explain the structure of sub-marine volcanic ejections; and after mentioning what has been called intrusive trap,' the author proceeds to another and a very ancient class of trap rocks,' which has been little adverted to by writers, though touched upon, as we have shown, by Dr Townson and by Mr Aikin.

'These are the rocks named in the following chapters "volcanic grit," "bedded and contemporaneous trap," and which I undertake to prove were formed at the bottom of the sea, during the accumulation of the sedimentary matter with which they are associated, particularly in the lower strata of the Silurian system. At one place these appear as currents, or sheets, of pure volcanic materials; at another they envelope marine remains-pebbles, sand, and fragments of rocks. Some layers consist of finely levigated volcanic scoriæ, passing into sand; and all these varieties alternate, so equally and repeatedly, with beds composed exclusively of shelly and marine sediments, that no doubt can be entertained that the diversified masses so arranged in parallel strata, must have been formed during the same period of igneous action.'-P. 172.

The author soon found that it was absolutely necessary, to the effective elucidation of the Silurian groups, to study and describe anew the several coal-fields included in the area examined, and to explain their relations to the surrounding deposits; but he could scarcely estimate the additional exertions thus required; 'for, with the exception of the basins of the forests of Dean and ' of South Wales, none of these coal tracts had been described.' Again, to complete the history of his region, it was necessary to examine all the rocks of igneous or volcanic origin,

* Smith's Memoir of Geological Map, p. 49.

VOL. LXXIII. NO. CXLVII.

B