In a paper read before the Geological Society on the 23rd of April, 1856, I referred to the proofs of a “plasticity,” or imperfect liquidity, in the crystalline igneous rocks at the time of their protrusion, and called attention to the mechanical changes, in texture and structure, which could not fail to have resulted from the mutual friction of the component crystals or granular particles of these rocks, during changes of volume or of position, occasioned by variations in their temperature while subjected to intense and irregular pressures.

In illustration, I referred to the “ribboned” pitchstones and trachytic lavas of Ponza, Ischia, Hungary, Mexico, &c., in which this structure had unquestionably been produced in that manner, and I repeated the opinion (to which more than thirty years back I had given expression), that to such internal friction of the component crystals, was probably owing the foliation of gneiss and mica-schist; through the “squeeze and jam” to which the lateral portions of an eruptive granitic axis must have been subjected, between its own expansive force and the resistance and pressure of the overlying strata.

The subject has so important a bearing on Geological Dynamics and the doctrine of Metamorphism, that I trust to be excused for carrying the inquiry a little further. In doing so it will bo well to begin by some elementary considerations.

It is the well-known property of most substances to pass from a solid to a liquid state, and vico versâ, under varying circumstances of temperature and pressure.

It is an old remark, that much of the prosperity attending the manufacture of iron in Great Britain has resulted from the circumstance that the ore, the fuel, and the flux are mostly associated minerals in the same locality; and, although this is typically true as regards the mineral basin which forms the subject of the present article, it is some-what curious that, in all probability, the discovery of the fuel in this instance dates much posteriorly to the employment of the ore, so that iron-making, had become an active branch of industry in this district long prior to any of the numerous seams of coal being worked; and, what is equally likely, before even their existence was known. If we look into any of the early histories of Gloucestershire, we find that, while abundant mention is made of the iron-mines and the smelting furnaces, no notice whatever is afforded of the coal, fully warranting the supposition that the discovery of the deposits had not then been made. I t will, perhaps, form an interesting preface to this paper, if, in connection with this latter circumstance, before entering upon the geological and lithological features of the ironstone formations, which are special and of the greatest interest, I give a sketch of the commercial history of the locality, past and present.

In tracing the progress made in the metallurgy of iron in this country, the Forest of Dean claims to have been among the first localities where the manufacture of that metal was established.

In our second group are provisionally assembled a number of Tere-bratula-shaped species, with a curved hinge-line, no defined area, beak entire, or truncated by a circular foramen for the permanent or temporary passage of a peduncle, and with spiral appendages directed outwards, as in Spirifera, but connected by a more complicated system of lamellæ. Much has, however, to be discovered concerning the interior details of the larger number of the species before we can hope to establish permanent and satisfactory divisions in this group.

The genus Athyris has for years attracted the notice of palæontologists, but it. was not until a recent period that all its important characters could be established. The species vary considerably in their external shape; they are circular or angular, elongated or transverse, smooth, ribbed, or striated, some have the entire surface of their valves covered with numerous concentric plates, which are prolonged in many instances nearly an inch from the surface of the shell, while in other species the valves are covered by a vast number of scaly ridges from which radiate closely-set fringes of elongated, somewhat flattened spines; and so close are these sometimes in their arrangement, that no portion of the shell can be distinguished.

Until of late years, the South Wales coal-field was considered to be very barren in fossils, and those few which were known were all thought to be of land or fresh-water origin. During my endeavours to work out the geology of this district for the last four years, I have, however, discovered sufficient to redeem it from such a reproach, and to prove that not only are there fossils, but that these are even in great numbers and variety.

The basin, which occupies portions of Monmouthshire, Glamorganshire, Breconshire, and Carmarthenshire, may be separated into two great divisions, both geologically and chemically. The first is the division into upper and lower coal-measures, separated by a thick mass of Pennant sandstone, or grit, while the chemical is the division into bituminous and anthracitic coals. The upper measures are principally found in Glamorgan and Carmarthenshires, the only coal-seam of that series in Monmouthshire, being known as the Mynyddswlyn vein. Westward of the Taff, however, which is the boundary between the two countries, the upper measures appear more frequently, and in more regular sequence; while, in Carmarthenshire, we obtain a complete section of these beds down to the Pennant rock, in the neighbourhoods of Llanelly, Penllergare, and Lloughor. The middle, or Pennant rock series attains its greatest development at Swansea, where it is 3,000 feet in thickness, and presents several important beds of coal; but in the eastern portion of this field they are very much thinner, and contain little or no workable coal. The summits of the hills which bound the parallel valleys on the north crop, are nearly all capped with this grit, which adds much to the peculiar configuration of the country, and gives a certain identity of outline to its general features.

We think it may prove useful and interesting to the geological student if, from time to time, we give a brief sketch of the Geology of some of the more famous localities in England, adding directions where to go, and how to work—which, to say the least, will be a great saving of time and labour, and enable those who are anxious to visit rich and instructive fields of research to make the most of perhaps only a brief holiday—a matter of no little moment in these days of almost unceasing toil.

The lovers of nature who live in the smoky atmosphere of great towns, shut up day after day in a close counting-house, enjoy a ramble amongst new or favourite haunts all the more on this account; and it matters not whether they are naturalists, geologists, artists, or merely admirers of the picturesque—the relish for their particular hobby is more keenly felt because it can be rarely indulged in, even if many difficulties stand in the way.

Few persons who have a scientific turn have unlimited time and means at their disposal; and, therefore, to the majority in such a case it is of some consequence to see as much as they can, and take the shortest route to their destination. The rapid and comparatively cheap means of transit afforded by the railway is equally available both for business and pleasure; but where science is the object, it is not always easy in a new country to find out the best and most productive places, and a few hints from any one who knows them well are invaluable.

The view from the summit of Cader Idris is one of the most magnificent in Wales. Turning to the south, the landscape consists of a series of rolling hills, stretching as far as the eye can reach, in smoothly swelling outlines; and it is impossible not to be struck with the circumstance that, though some rise higher than others, they maintain a sort of average height, accompanied by a general gentle inclination towards the sea. Through this broad undulation innumerable valleys have been excavated. The hills have not been formed merely in consequence of disturbance of the strata; but, through the outcropping and smoothed edges of disturbed strata, many great and small valleys have been cut by old marine denudations, atmospheric disintegrations, and the action of running water. The general uniform character of the outlines of this country is due to the sameness of the rocks, which, in the main, consist of slates, occasionally varied by hard or interstratified bands of sandstone, the whole belonging to that part of the Silurian series known as the Caradoc or Bala beds, and the rocks immediately overlying.

Turning northwards, a change in the character of the landscape becomes at once apparent. The mountains are broken and rugged. The summits of the Arans, the great swelling mass of Rhobell-fawr, the cliffs of Rhinog-fawr and Rhinog-fach, that guard the pass of Bwlch-drws-ar-Dudwy, the bold outlines of the Arenigs, the Moelwyns, and Cynicht, all meet the eye almost at a glance; and, far in the distance, the peak of Snowdon sharply pierces the air, rising to a height of 3,571 feet above the sea.

Having reviewed, in our first paper on this subject, the tipper portion of the Lower Oolite, down to the Stonesfield slate inclusive, we propose in this to give some account of the lowest member of this formation, the Inferior Oolite, and then to pass on, in descending order, to the Lias. The district under consideration has, of late years, been very generally and carefully examined by many able and experienced geologists; but nevertheless additions to our knowledge of its Geology are from time to time being made; and our own practical experience in the field confirms the belief often expressed by others, that, however much may have been done in any particular spot, there is always something left to reward intelligence and zea

The student, however, must not be discouraged at being at first able to add but few new facts to the list; he must bear in mind that one truth well authenticated is worth a hundred hasty generalizations and unfounded conclusions. The book of Nature is open to all who choose to read it; and he who, studying it in an honest and earnest spirit, adds something to the stock of general knowledge, even though it should be but a little, yet that little is worth recording, and is deserving of support and encouragement from the scientific public. Without actual reference to the wonderful revelations of Geology, our great poet, Shakespeare, has said, almost prophetically, that there are “sermons in stones, and good in everything;” and, certainly, the geological student may literally adopt this motto.

The coal-measures repose conformably on a series of grit-beds, all more or less charged with oxide of iron, and measuring together about 500 feet in thickness. In some places a bed of limestone intervenes between the lowest bed and those above, but the general section, in descending order, is as follows:—

1. Coarse red grit-stone, called “The Miner's Farewell Rock.”

2. Light red sandstone, with layers of variegated marls, which, although partly indurated in the bed, fall to pieces by exposure to the air.

3. Fine-grained quartzose grit, much charged with iron in the middle beds, constituting the “Sandstone Mine Formation.” In this group there are two thin beds of coarse conglomerate, or pudding-stone.

It would be impossible for me to enter into any adequate description of this most important part of the Forest geology, without extending this article to an undue length. The following summary, therefore, must suffice, in the present instance; although I purpose describing the coalfield, which has special interest—geological as well as industrial—on another occasion.

If the ordnance geological sheet No. XLIII. S.E. be examined, with the horizontal sections Nos. 15 and 16, a very good notion of this coal-basin may be obtained, although not too much dependence is to be placed, practically, on the position of the lines marking the crop of the several veins. Indeed, to lay down the line of crop accurately, in many places where there are no workings, is impossible, from the thickness of the over-burden or soil: besides which, the theoretical lines invariably require to be shifted, from the occurrence of minor faults and local denudation.

Perhaps in all the physical geology of England there is nothing finer than the erupted heights of the Clee. Encircled by the typical “Old Red”—a wide-stretching tract of alternating sandy shores and gravel-beaches of that period—are the characteristic beds of the coal-measures, lying upon Millstone Grit and Mountain Limestone.

Of the causes that have elevated these deposits into the hills of Titterstone and the Brown Clee I need not speak—their basaltic summits, where the erupted rock has assumed a rude columnar form after cooling, are sufficient evidence; but I would direct especial attention to that group of beds whose strike is along the Oreton ridge, and whose chief member, the Mountain Limestone, forms its axial line. This lies midway between the two hills; its southern side slopes down the “Common,” and is composed of Millstone Grit, cut off abruptly by a long line of fault, the effect of which has been to have depressed that deposit into a valley, and to have raised the underlying “Old Red” into a nearly continuous line of cliff. The accompanying section will better describe their relative positions.

These Millstone Grits are non-fossiliferous; but the mineralogist may detect in their conglomerated structure many pebbles of a high class, jaspers and cornelians of pure quality being often met with. These beds lead up to the Mountain Limestone, which contains a fine series of organic remains, such as palatal teeth of the Cestraciont fishes. Petalodus Hastingsii and Psammodus porosus are abundant; yet, although fragments of their jaws are not uncommon, I have only met with one specimen having the teeth in their true position.

All that pertains to the science of Palæontology is of consequence to the geological inquirer; therefore a few notes and illustrations relative to the Brachiopoda may, perhaps, prove acceptable to the general reader, and, at the same time, stimulate some others to prosecute an inquiry upon which so much time and labour have been already expended.

It was justly observed by a distinguished naturalist, that there exists a decided advantage in the same subject being investigated by a number of different observers; and the truth of this statement has been fully substantiated by the information already acquired on all that concerns the affinities, classification, and anatomical structure of the Brachiopoda. But it must also be remembered, that, although these topics may have been individually and collectively the subject of considerable investigation, much still remains to be discovered and satisfactorily explained before many of the problems relating to the character and history of the class can be considered as finally determined.

All palæontologists seem to agree that the Brachiopoda should bo divided into two principal groups. The first will include all those genera and species which have their valves articulated by means of teeth and sockets; the second will comprise those forms which, being un-articulated, have their valves kept in place by means of muscular and other contrivances.

One of the most remarkablo fossils assumed to be distinctive of a particular geological horizon, and which, from its very striking outline, most readily impresses itself upon the mind, is the Rhynchonella acuta of the Lias-marlstone, a Brachiopodous shell common at Stinchcombe, Churchdown, and other localities of this district, and well known elsewhere. Having paid considerable attention to the class to which it belongs, I have long abandoned the common practice of placing in the cabinet only those specimens which chance to accord with the forms figured and described as typical. Instead of doing this, I have selected, as good examples, those which manifestly have not been crushed or injured prior to their entombment and petrifaction; and these I have arranged in series illustrative of specific development.

This mode of procedure has taught me that the species under consideration assumes forms varying from that under which it is most generally known; and it has led me to believe that several so-called species of various authors are, in reality, mere varieties of this.

All who have attentively studied the numerous Terebratulidæ of the Cotteswolds will have experienced the difficulty of assigning satisfactorily certain anomalous forms, occurring in beds ranging vertically from the Pisolite, or even lower, to the Cornbrash, to such well-established species as Terebratula maxillata, T. perovalis, T. globata, or T. intermedia, and will remember the remarkable varieties of individual character presented by other species, as, for example, T. plicata, T. simplex, T. fimbria, and T. carinata, sufficiently striking when studied in solitary examples, but, in an extensive series, not suggestive of good and stable specific differences.

The Geologist, which this day makes its appearance as the popular organ of a Science which has of late years advanced with gigantic strides, and which is daily attracting an increasing share of attention from all classes of society, enters upon an unoccupied field. Its object is to supply a deficiency in scientific periodical literature. We say this in spite of the sneer which has often been uttered to the effect that no new periodical was ever issued which did not profess “to supply a long felt want.” Of course new periodicals profess “to supply a want;” they are got up for that purpose; should those who bring them out think they are not “wanted,” it would be sheer folly to produce them. With regard to The Geologist, there is abundant evidence that such a periodical is needed; evidence which rests not on our own judgment alone, but on the concurrent testimony of many eminently able and practical men, who have expressed their gratification at the announcement of a magazine, based upon the plan we have projected. We therefore venture to launch our first number with the full conviction that we are about to supply a work which will prove to be in a high degree useful.

In entering upon this undertaking, we desire to enlist the sympathy and aid of all lovers of Geology.

The name “Iceland” raises ideas, especially in the winter time, the reverse of cheering; and a subsequent low average of fingers and toes suggests itself as no very unlikely price to pay for witnessing the marvels of Thing Valla. Gentle reader! what think you of an al fresco breakfast taken on the plain, “in shirt-sleeves, with a white handkerchief wrapped round the head for fear of the sun, the whole landscape gleaming and glowing in the beauty of one of the hottest summer days I ever remember?” Such is the description given of the summer climate as the party encamped to examine the place more in detail.

Descending the gorge of the Almanna Gja, they went towards the lake. “The perpendicular walls of rock rose on either hand from the flat greensward that carpeted its bottom, pretty much as the waters of the Red Sea must have risen on each side of the fugitive Israelites. A blaze of light smote the face of one cliff, while the other lay in the deepest shadow; and on the rugged surface of each might still be traced corresponding articulations that once had dovetailed into each other, ere the igneous mass was rent asunder. So unchanged, so recent, seemed the vestiges of this convulsion, that I felt as if I had been admitted to witness one of nature's grandest and most violent operations, almost in the very act of its execution. A walk of about twenty minutes brought us to the borders of the lake—a glorious expanse of water, fifteen miles long, by eight miles broad, occupying a basin formed by the same hills, which must also, I imagine, have arrested the further progress of the lava torrent. A lovelier scene I have seldom witnessed. In the foreground lay huge masses of rock and lava, tossed about like the ruins of a world, and washed by waters as bright and green as polished malachite.

I. “Il suffit de parcourir des parties très circonstrites de la surface du globe, pour voir qu'elle est composée de matériaux très-variés.” The most striking of these differences were, of course, noticed even in the least civilized times; and, as observation advanced, and experience accumulated, the minor and less obvious variations of constitution and texture were gradually reduced to order, and classified into the science of Mineralogy.

II. So far our science concerned itself merely with what we should now call a correct description of the mineral character of rocks, without entering into the question of their genesis or mode of origin. But at the dawn of geology—that is, when men first conceived that the various rocks and strata at the surface of our earth were formed at different, and often immeasurably remote periods—then the study of rocks entered on a new phase. The age and succession of these formations were judged, in the first place, from the order of their superposition; and when it was found, as a general rule, that each formation, or stage of this succession, was marked by rocks of a specific mineral character, it was hastily concluded that this mineral character was typical of their age, and that the latter could be deduced from the former: nor was this generalization devoid of broad principles of truth; the ancient and more recent formations are each undoubtedly composed of rocks of very different mineral character—the former being made up such of rocks as granite and the so-called primary limestones and clay-slates, while the latter consists of clays, chalk, or slightly consolidated sandstones.

In my former paper I endeavoured to describe the general appearance and characteristics of the limestone, millstone grit, and Pennant rocks of this coal-field, and shall now proceed to give a brief outline of the coal measures themselves and their fossil contents. As I stated before, the character of the coal is materially different in different parts of the basin; for instance, if a line be drawn from Merthyr to the sea in a south-western direction, it will divide the basin into two unequal portions, the eastern one containing bituminous coal, and the western the anthracite. I do not mean to say that there is an exact line of demarcation between the two kinds of coal, but merely that such a boundary will seem to show pretty well where the two qualities pass into one another. Curiously enough, too, in the western or anthracite portion the seams are anthracitic in the northern bassets, while the southern outcrops of the same veins are bituminous. The anthracite is now in very great demand; but, formerly, people would have nothing to do with it, and there was even a law passed to prevent its being burned in London, on account of its supposed noxious qualities, and the idea that it was detrimental to health. It differs from the bituminous coal principally in containing more carbon, less bituminous matter, and less ashes; and, as a consequence, is a much cleaner-burning coal. We may, however, dismiss the anthracite, as this portion of the field is destitute of it.

Reader, have you ever visited the far-famed Lakes of Killarney? If you have not, by all means go there; and if you are a geologist as well as a lover of beautiful scenery, the pleasure of the visit will be greatly enhanced.

There you have lofty and rugged mountains (some of them clothed with wood nearly to the summit), from whose sides gush limpid fountains, increasing in force as they descend, and in their onward course madly leaping down the steep cataracts, until they are at last lost in the majestic lake beneath,—the admixture and variety of the whole being beautifully harmonized and softened by the extraordinarily luxuriant foliage of thousands of plants, from the stately oak, the bushy arbutus, and dark green holly, to the humble but graceful “London Pride” (Saxifraga umbrosa), the abundance of which seldom fails to attract the notice of the most casual observer.

The mountains are formed of rocks of the “old red sandstone period,” the upper division of that group or “yellow sandstone” being generally observed at the foot of the slope, this being again overlaid conformably by the “mountain-limestone,” which extends in many a contortion over the plain.

In the rocks of the “old red sandstone” a geological eye will at once be struck by the fine examples of glacial action exhibited in the scratches and groovings of their surfaces, caused by the sharp edges of blocks and fragments of other rocks, contained in icebergs, having passed over them; such markings being, for a considerable extent, parallel, or nearly so.

With the exception of the very able memoirs drawn out by Sir H. de la Beehe, in the “Geological Survey,” Vol. I, and the sections of the same survey, as compiled by Mr. David Williams, no coal-field has been so little described or worked out as that of the South Wales basin. Although the work of a master geologist, yet the very nature of these memoirs, describing the general arrangements of the rocks in the southwest of England, altogether precludes any attempt at minute geology, which, indeed, should mostly be supplied by local workers. Other coal-fields have been ably and intimately described, but this particular field only in very general terms. Why it should be so I know not, unless it is that only of late years its vast resources have been opened up, and that its many romantic vallies, teeming with beauty above and brimful of coal and mine beneath, have been made accessible either to the tourist or the mining adventurer. Every year, however, sees new railways opened in Monmouthshire and Glamorganshire; and I have little doubt but that the completion of that magnificent work, the Crumlin viaduct, has done more than anything else to attract persons to that part of South Wales, either from a love of the beautiful, or the scientific interest attached to it. For the study of practical geology in its several aspects, this coal-field possesses many advantages, particularly in physical geology and the peculiar manner in which sections are obtained, owing to the nature of the ground.

The next division, 8th, consists of a bed of fawn-coloured sandstone of about ten feet in thickness, containing nodules of rag, with Pectines, Terebratulæ, Rhynchonellæ, &c., in the lower portion, which, owing to its softness and looseness of texture, the weather wears away, leaving the shells finely exposed. It is chiefly owing to such excavation of this bed, by the combined influence of the elements, that those great falls of the superincumbent masses have taken place at intervals along the line of the Undercliff, many such “founders” having happened within the memory of residents, and others being likely to occur constantly from this hard and solid mass of strata resting on an insecure foundation, the effects of which are still further increased by the presence of the Gault below.

But a few years back a large mass near Blackgang thus assumed such a dangerous and threatening attitude, by the lower part of it being so much worn away, that the authorities blew it down with gunpowder. Many thousand tons of rock and debris were thus thrown down, completely blocking up and destroying the original road; one huge mass still stands close to the road, as large and as high as a good-sized cottage.

A layer of rag-stone, called the “Big Rag-bed,” containing fossils, terminates what is termed the “sandstone-group.”

As the Lias in this county is a very bad material for economical purposes, it is not often extensively quarried; and, considering the few available sections, the number and variety of organic remains which have been, from time to time, collected, are really remarkable, and show the prolific nature of the sea of that period. Some localities in that sea, of course, would be richer than others, as is the case in the present day; but, on the whole, this formation is everywhere marked by a great abundance and diversity of fossils. The Palæontologist often looks with a longing eye at some old quarry, long since closed, which had been at one time famous for its zoological contents, and speculates upon the wonders which lie concealed beneath his feet; and he restores in thought some ancient monster of the deep, some curiously-formed shell, or some strange plant; and perhaps, if he had the power, he would dig away, in the hope of possessing some of these treasures which his imagination has conjured up before him. And yet, after all, such speculations are not so imaginative or unreal as they may at first sight appear, for the strange and extraordinary forms of extinct life, which the extended researches of scientific inquirers have brought to light, seem to justify the highest flights of fancy; and none can tell when or where some wonderful relic of the past may be found.