It is one of the many striking facts of geology that, as we pass from one great group of rocks to another, we find a considerable change both in lithologioal and zoological characters. Sometimes the transition is abrupt and sudden, at others, slow and gradual. In the former case, the marine fauna of the older deposit had perished, and a new race sprung up and succeeded to its place; while, in the latter, there was only a gradual dying out of some species unable to exist under the changed oceanic conditions, others more hardy still continuing to flourish in the later formation. But this change of genera and species is not confined necessarily to the breaks which seem to have taken place between one great rock-system and another; it is often to be noted in a greater or less degree, as we have seen in our review of the Oolites in this county, in the minor divisions and sub-divisions of each formation. The student must also bear in mind that the strata which form the crust of the globe were, for the most part, deposited by the sea; a very small proportion only being the products of fresh water, and still fewer being purely terrestrial. Therefore, in our researches into the history of the past, we have to deal more usually with the varied inhabitants of the ancient seas, and to mark the changes which took place from time to time as we pass through either entire periods, or the parts and details into which they may be divided.

II. It is about a mile across the Lower Lias, on which the villages of North Cave and Hotham are situated, to another gently-rising ground which ascends out of Hotham Park to the eastward in a beautiful sloping bank, and being tastefully planted with stately trees, contributes very much to the charm of the scenery. Coming in with my hammer to the ancient village, in the bright and odorous evenings of midsummer, I have often been arrested by the sweetness of this place; and, enamoured of its serene and peaceful beauty, I have loitered to admire its dark plantations, and the greensward slope that I am now describing, and the illuminated wold rising high in the distance. It is the low escarpment of the Middle Lias which declines thus pleasantly into the park at Hotham. A.s we go out of North Cave towards Beverley, this bank may be observed to rest upon soft blue shales, which have hitherto supplied no fossils. When we begin to ascend it, we may turn into a copse on the right-hand side and study the section in a marl-pit, or we may notice the roadside cutting. In either case, we shall observe that the beds change as follows:—From blue shales at the bottom and lower part of the ascent, through brown earthy-looking shales and sand with irregular broken bands of nodular clay-ironstone, one of which enclosed a cast of Unicardium cardioides, to a hard rock-bed of the true Marlstone, two or three feet in thickness, which again is capped at the top of the ascent by a very rusty, rubbishy, and ferruginous rock.

The unstratified Plutonic rocks are considered to form, as we have intimated, the common base of the stratified beds all over the globe. With them, however, we have little to do in this place. Our labours commence with the stratified, and we should even have excluded the so-called “Azoic,” had not that term been recently subjected to considerable restriction by the discovery of organic remains in some of its members; and, as it is still likely, by further researches, to be totally absorbed into the Palæozoic system, we append an ideal section representing the sequence of formation of the most ancient groups of fossiliferous rocks, with the relative position of those primordial conglomerates, flags, and schists in which as yet no organic remains have been found. Whether, at the vastly remote period at which those isolated masses, still ranked as Azoic, were formed, the advent of life had really not taken place on our planet, or whether those masses are the few remnants of a still older stage of our world than any presented to us by the recognised series of fossiliferous rocks, has yet to be determined by the investigations of geologists—but in their massiveness and their vast age they must ever be regarded with veneration and wonder.

The Llandovery rocks were so named by Sir R. Murchison from the locality in South Wales where they are most fully developed, and where their physical relations to the formations above and below them are clearly exposed. Those rocks constitute an intermediate place in the Silurian table, connecting, by some of their contained organic remains, the fauna of the upper and lower Silurian groups. The upper Llandovery rock contains many shells common to the Wenlock beds, and is considered to form the natural base of those deposits; on the other hand, the lower Llandovery is related by its fossils to the Caradoc beds below, and both members of this formation are united by having certain fossils in common and peculiar to them, but are chiefly characterized by the abundance of some species of Petraia, Atrypa, and especially Pentamerus. This group consists of soft, argillaceous sandstones and building stones (Goleugoed), shales, some calcareous bands, hard, coarse grits, and quartzose, pebbly conglomerates. Thickness 2,000 to 3,000 feet.

Localities.—Both members of this group, and their relations to the overlying and subjacent rocks, are well exhibited at Noeth Grüg, near Llandovery, South Wales. In Radnorshire, Shropshire, and Hereford, the upper member, or Pentamerus oblongus zone, is alone present, and is seen in some places to be unconformable to the Longmynd and Caradoc rocks. The conglomerates of the west flank of the Malverns, and the sandstones of May Hill and Huntly, Gloucestershire, are of this age.

Hotham is a small village between the towns of South Cave and Market Weighton, in the East Biding of Yorkshire, situated upon the Lower Lias formation, about five miles above where that zone crosses the Humber at Whitton and Brough.

Several interesting rooks of the secondary series pass by this village, generally in bands of inconsiderable thickness, and in a direction nearly N.W.N. In most other districts widely separated, they can here be examined near a single point; for we can walk in about two miles from the New Red Sandstone, across the Lias and Oolite, to the top of the Chalk. And as these rocks are, in part, little known, and, in part, have been long held to be exceptional and peculiar—moreover, as they seem to me to throw light upon questions not quite settled at the present time—such as the existence of the Bone-Bed and Insect-Bed, at the base of the Yorkshire Lias, and of the Inferior Oolite in the long litigated neighbourhood of Cave—I am induced to offer some observations upon them, which I made at Hotham during two very short vacations, and which, I trust, will be found to be of general, as well as of local interest. The purpose of this paper will be, to compare some of the most important formations occurring near Hotham with the same formations as they are more typically represented, and more familiarly known, in other parts of England.

The two following species appear to me to be new, and come likewise from the carboniferous limestone:—

1. Hydreionocrinus Woodianus. De Koninch. Pl. IV. fig. 5, 5a.

The head of this species is of medium size, sub-cylindrical in form, and terminated at its upper part by a crown composed of fifteen pieces, disposed in a circle, and attached one to another, the central space being occupied by the dome. The calix, taken by itself, resembles a little open cup. The base is composed of rather small plates, most of which have a point attached to the stem. The subradial plates, with the exception of that on the anal side, are much broader than long. They are very thick and strongly arched, and consequently their sutures are very decidedly exhibited. The first radial plates are pentagonal in shape, about a third broader than long, and, like the preceding, rather thick, and separated from each other by a strong groove. The second radial plates are also pentagonal, and broader than long. The axillary plate is very thick, and furnished with a slight protuberance, and juts outwards. The brachial plates, which follow the axillary plate, offer nothing remarkable. The external surface of these plates is indented with little irregular tracings, which make it rough, and the test thus resembles shagreen. The arms—twenty in number—are composed of cuneiform alternating articulations, and are joined together laterally. I have not observed any traces of pinnules. The little plates of which the dome is composed are all ornamented with a prominent tubercle in the middle. Their surface is apparently smooth, their number variable, and their form is generally hexagonal. I have not been able to discover any traces of a horn or proboscis, nor of any anal or buccal opening. It is probable these were situated between the arms, which were placed on the anal or irregular side of the bulb, and that these arms were capable of extension, and of admitting a passage for the food of the animal. The stem is rather stout, in comparison to that of most of the other species, among which it is often very slight.

In the preceding exposition the object has been to give, in a condensed form, the leading facts and conclusions of geology. These facts are so firmly established by observation, and the conclusions from them so clearly demonstrated, that every rational mind must assent and be prepared to admit the principle on which Geology, like all physical sciences, must rest—that geological phenomena must be referred to physical causes.

When the student has obtained sufficient familiarity with these established propositions, he will be prepared to follow in the discussion of the less elementary problems of the science, many of which are subjects of controversy. Before, however, going into these speculations, Mr. Hopkins devotes several pages to the evidences of the vast antiquity of the globe, dwelling both on the evidences afforded by the organic remains of successive creations embedded in the rocks, and on those drawn from the inanimate kingdom. Of the first we find that an immense number of different tribes of animals and plants which in former ages have given their passing phases to terrestrial life on our planet have disappeared with a transition so slow that, according to the present order of nature, there is not the slightest evidence of the introduction of a new species of animal since the creation of man; whilst of the latter, it appears certain that the deposition of sedimentary strata, and that process of denudation necessarily contemporaneous with it, must have proceeded at very much the same rate in former as in recent times; and, admitting this conclusion, we obtain something like a rough conception of the enormous lapse of time necessary for the deposition of the whole mass of sedimentary formations, by simply comparing such mass with the proportion which has been transported and deposited, within the last two or three thousand years.

A notice of the geology around Killarney having already appeared in the Geologist, by “A Brother of the Hammer,” it will be sufficient for us to indicate the best localities for sections and fossils, premising that the upper and lower Old Red Sandstone are unequivocally represented in Ireland, independently of the upper groups of conglomerates, and red and yellow sandstones.

The Old Red Conglomerate in Ireland is in many places unconformable to the Old Red Sandstone, and constitutes the base of the carboniferous deposits; and I had been assured that the same unconformability had been detected in the Forest of Dean; but a careful examination, with Dr. Melville, has since convinced me that there is no such unconformability between the Upper Brownstones and the overlying masses of conglomerates and red and yellow sandstones in this or the Blorenge district. In Ireland the local geologists persist in limiting the term Old Red Sandstone to a series of deposits which there, most certainly pertain more to the carboniferous group, viz., the conglomerates, red sandstones, and yellow and grey sandstones, which pass upwards conformably into the Coonahola grits and carboniferous slates. The equivalents of our cornstones and brownstones of Brecon and Monmouth may be studied at Glengariff, at the head of Bantry Bay, where the lowest rocks seen are the Glengariff grits, or upper cornstones, overlaid by the Dingle slates or brownstones, and the red sandstones of the conglomerate series, with no unconformability.

Searching for coal is, not only at home but also abroad, a serious subject, and one in which the practical utility of connecting geological knowledge with active operations is particularly obvious, and which from actual experience I can well illustrate by many interesting cases which have come under my own notice. The first determinations in a coal “adventure” may be classified as follows:—

1. Where coal is not. 2. Where coal may be, but at too great a depth for working. 3. Where coal may be found convenient for working. 4. Its quality and extent.

In order to make what follows the more interesting, we may premise, what every Geologist now knows—that the earth is made up of strata of different kinds—e.g., sandstones, limestones, and argillaceous beds called rocks. The different strata have been formed step by step, layer upon layer. Each stratum has its distinct position and age in relation to other strata. The relative age and, consequently, position of a rock can be distinguished by mineral structure, fossil contents, or both.

Again, by way of still more clearly establishing our primary position, let the following table represent some of the strata above and below the general coal deposit:—

Now this partial table of British strata represents the coal measures as being overlaid by the New Red Sandstone deposits, and underlaid by the Mountain Limestone and Old Red Sandstone, which, though a general, is by no means the invariable rule in coal deposits, as sometimes the Mountain Limestone is absent, and the coal measures rest upon the old red system, as in great part of the Shropshire coal-field.

The divisional line of the “Bottom Rocks” is not, however, to be placed at the point at which life first appears. This great series is naturally divided by differences of mineral conditions, by order of deposition, and in reality of age, in our own country, and in other countries both of Europe and America, and apparently also, as far as our present information goes, in Asia and Africa.

In Canada, below the equivalents of our Shropshire “Bottom Rocks” and of our lower Cambrian beds, as in the Highlands of Scotland, as we have already obtained, are still more ancient beds of sedimentary origin, which have become crystalline. In Bohemia, in Finland, and in Scandinavia we have these primeval gneissic lands below the lowermost Silurian deposits; but the geologists generally of other countries, except, the Canadian, have not yet made much progress in this investigation, and it is only in very few instances that the distinctions between the older and younger gneiss have been noticed; and so little regard as to geological age has been ordinarily paid in the case of granitic rocks, that, knowing as we do the very various periods at which some of those masses were erupted, or protruded through sedimentary strata, the mere knowledge of their existence is nearly or quite valueless as evidence.

The disposition of the coal measures is pretty generally known by most persons who have paid any attention to the science of Geology.

It will not, therefore, be necessary for me to describe their position or the place they occupy; undoubtedly they are of very ancient origin, being nearly allied to the old red sandstone, amongst which some of the fossils, or rather similar fossils, have been found, which I am about to describe.

Hugh Miller is the great authority regarding the old red sandstone deposits; no man laboured here with more assiduity than he, and is is my regret that I have not, as yet, informed myself more as to his labours. His recent posthumous work, the “Testimony of the Eocks,” alludes to some fish remains which Scotland has produced; but Professor Agassiz is still more eminent as it regards this interesting class of fossils.

I said interesting, for I had no conception that fish remains could have been rendered so remarkable, and this may be owing to the delicate and soft nature of the mud in which they have been laid. I cannot imagine that my readers should be so captivated with these remains as myself, for there is a peculiar interest felt by all those who conduce to any new discovery; and the more any science is studied the more fascinating it becomes, particularly if we have been led into it by an intimate knowledge of its mysteries from actual observation.

There are many localities around London which possess features of interest to the geologist, that can be reached and examined on a single day. Such a one is the pretty little town of Bromley, in Kent, with a population of 4,000 souls, at a distance of ten miles from London Bridge, and now within easy reach by the Mid Kent Railway, only just opened. A mile to the north-east of Bromley is Sunderidge Park, in which is to be seen a section of the well-known oyster-conglomerato rock, in a large pit which, together with the accompanying shingle, has been quarried for various purposes for many years. This spot is noticed by Dr. Mantell in his charming volumes, as one of the most interesting localities he was acquainted with. At and around Bromley is an area of some extent, formed by the Lower London Tertiaries; a small patch of chalk, however, crops out to the east of the town, in which are some ancient quarries. One of these possesses some interest from being underground, and containing, as I was informed, several intricate windings.

The London clay, with the underlying plastic or Woolwich clays, and Tnanet sands, constitute the lower division of the Eocene strata of the Tertiary group of rocks. The London clay extends over several counties of England, constituting a large part of the soil of Essex, nearly the whole of Middlesex, and portions of Berkshire, Surrey, and Kent.

Dr. Phipson, of Paris, has drawn attention, in the April number of the Geologist, to the observations which have been made of the presence of mercury in the soil and substrata of the town of Montpellier, and, in your June number, another correspondent notices the finding of the same metal under circumstances so decidedly adventitious, however, as to possess, I think, rather archæological than geological interest. The occurrence of this precious metal in rocks and mineral deposits of such ages as we should hesitate to assign for its matrix, most probably arises from its fluid nature admitting of its easy transport to distances far remote from those formations in which it exists in situ; and, as furnishing something like the history of its presence in such apparently abnormal situations, the following account of its discovery at Ajaccio, in the Island of Corsica, may, perhaps, be considered worthy of insertion:—

In the year 1811, a M. Matthieu, an Engineer Officer of the French Army, was entrusted by Napoleon with the mineral survey of the Island, but, being re-called to his military duties in 1814, was cut off before Leipzig, leaving in the possession of his widow the notes he had made of his survey. These notes do not appear ever to have been officially communicated, but among them was a memorandum to the effect that a deposit of mercury existed at Ajaccio.

The beds immediately below the Marlstone, which consist of laminated shales and clays often micaceous and sandy, were well exposed at the latter place during the formation of the reservoirs, and at Robinswood Hill, near Gloucester, and at Chipping Campden, on the north-eastern extremity of the county, a locality which deserves a special visit. In this part of the series, at the base of the Marlstone, a good deal of ironstone prevails, which, it is said, was in ancient times worked near Gloucester; it is of some thickness and of excellent quality at Campden. These beds are no where destitute of fossils, among which, at the last named place, we may especially notice the fine Ophioderma Gaveyi (one of the brittle-stars, some species of which are so frequent in our present seas) and a new species of Pentacrinites (P. robustus, Wright). Here, too, at the base of the Marlstone, Mr. Gavey found two previously undescribed forms of star-fish, the Uraster Qaveyi and the Tropidaster pectinatus, both of which were figured and described by the late lamented Professor Edward Forbes, in the 3rd Decade of the Geological Survey. With them he obtained an entire and beautiful large Cidaris Edwardsii (Wright), with the attached spines, a rarity in this condition in any formation, and especially in the Lias, where Echinoderms are very scarce; although we have met with specimens of some small species, with the spines attached, in the upper, middle, and lower Lias.

These fossil star-fish are often obtained grouped together, as living ones are now, with their short spines adhering to the rays. Indeed, they seem to have been more than usually abundant at this spot—at least, such is the case with the Tropidaster pectinatus. Two or three species of small Crustacea, chiefly belonging to the genus Astacus, were also procured there in the argillaceous nodules, irregularly distributed throughout the clay. The most interesting we have seen is one in our possession, nearly allied to the recent genus Æga, belonging to the order Isopoda, and which, like others of this group, was probably parasitic upon fish. There were also a great number and variety of marine shells in a remarkably good state of preservation, and these were equally abundant at Hewlett's Hill, some of them retaining the actual shell.

More things remain to be spoken of fossils; wonders of skill to be presented in their construction and design; marvels of mechanical devices for progression, for strength, for lightness, or for protection to be displayed; and consummate wisdom and benevolent forethought to be exhibited in their adaptation to the various purposes for which they were created—in fact, as much as we find to admire or to consider in the structure of existing animals or plants, in their means of developement or of growth, in the influences of climate and seasons upon them, so much also do we find for equal admiration and reflection in those ancient “medals” of past creations.

Even contorted and damaged fossils are not without their evidences.

Squeezed on either side or flattened, they do not merely ndicate the pressure to which they have been subjected, but the direction also from which it came. Everything connected with fossils is of high interest; but from first to last the value of fossils is in their teachings; and it is never by pounds, shillings, and pence that we can value them at all. In such a light they are but worthless bits of stone, as fit to mend the roads as to be saved. To minds that esteem them thus, they are no treasures, but merely merchandise. Properly studied, however, they convey their lessons of the past; and when regarded as letters in the vast and holy book of Nature, which must ever be read with solemnity and reverence, they take their places properly in the great sentences and wonderful passages of that mysterious language from which Geology interprets the order, wisdom, goodness, and prescience displayed in the animated worlds that were. It is thus we shall have attained to the true knowledge of the value of fossils, when we shall turn from such readings with adoration to the Great Author of all.