# A Treatise on Geology/Chapter 6, part 3

Post-Tertiary and Modern Deposits.
(Including "Pleistocene," "Diluvium," and "Alluvium."—" Superficial Deposits.)
Since the tertiary formations were completed in most parts of Europe and America, the energies of nature have gone on to accumulate over these and earlier deposits a great quantity of additional matter, under many varied circumstances. It is often extremely difficult to say, whether certain aggregations of sand, gravel, and shells, are of tertiary date, or the productions of later times: enormous heaps of pebbles and bones lie in particular situations, and are evidently of great antiquity; but whether of the tertiary era or not, requires much care in determining. Certain lacustrine deposits, full of shells, marls, peat, and bones of stags, cannot, by a hasty glance, be known from tertiary strata collected from ancient lakes. But, upon farther and closer scrutiny, geologists have generally agreed to think that a whole series of deposits, partly marine, partly terrestrial, ​lacustrine, and fluviatile, has been formed since the date of the truly tertiary strata.
The evidence for this opinion is absolutely conclusive, as to the great body of tertiary strata: it is past a doubt, that, since the age of the palæotheria in the formations of Paris, the same physical regions have been tenanted by wholly different races of animals. The same conclusion is equally and easily proved for the basins of London and Hampshire, and for many other tracts in Europe; and, if we did not inquire very scrupulously, these partial truths might be thought to justify a general inference that the tertiary strata could always be clearly separated from the overlying diluvial and alluvial sediments. But we must not disguise the real difficulty which occurs to the candid inquirer, who wishes to find out laws of phenomena as a basis for theory, rather than to rest satisfied with a conventional system.
By what rule of practice, or deduction from theory, does the geologist discriminate between the Sicilian tertiaries, with 95 per cent, of existing species of shells, and the conchiferous gravels and sands of Holderness and Lancashire, in which, among twenty species of shells now living in the German Ocean, one occurs which is not yet known? If the Lancashire shells are, like those of Speeton, Uddevalla, and the coasts of Devon and Calvados, raised beaches, and to be classed in the modern epoch, why are the Sicilian deposits ranked as tertiary? At what place in the scale of percentage of species is the line of division to be drawn, and how is this division to be justified?
The gravel which is spread over great surfaces in England, is called diluvial, and supposed to be the product of great but transient disturbances in the level of land and sea: for another example, the dispersion of blocks and gravel from the High Alps might be quoted as an effect of this kind, according to the view of M. Elie de Beaumont; but, if such be the effect of elevation of mountain ranges, may we not expect somewhere to find ​traces of a "diluvium" of tertiary, secondary, or even primary date?
Lacustrine deposits formed in and since the tertiary era, are not so clearly distinct even by position, as to allow us, in all cases, to be well satisfied about their date; witness the ossiferous beds of Weigh ton in Yorkshire, the Val d'Arno, Œningen, Gmünd, and many other localities.
Yet, notwithstanding these objections, geologists have for a long time recognised the classifications which are based on the principle that, since the tertiary era, marine, fluviatile, and lacustrine deposits have happened on the land in various parts of, at least, the northern zones of the globe; and though impartial researches have led us to doubt the practicability and advantage of this broad distinction, we shall now endeavour to develope the history of the "post-tertiary," or diluvial, alluvial, and modern aqueous deposits; reserving for the section on organic remains what general reasoning we are disposed to advance.
In one point of view, these deposits of post-tertiary periods are of the highest possible importance: they form the connecting links between the great phenomena of long past time, whose causes we are to seek, and the less obvious effects occasioned in modern nature by causes which are known. The post-tertiary accumulations consist of detrital deposits, reminding us of ancient conglomerates, lignitic beds like ancient coal strata, calcareous, arenaceous, and argillaceous layers, which are specially comparable with tertiary, and through them with secondary strata. On the other hand, almost every thing that we see among these deposits is clearly intelligible by study of analogous diurnal operations in nature; and thus it is desirable to include in one section the consideration of post-tertiary and modern aqueous products, and to reason on the agencies concerned, as if the whole were one connected series of events still in continuation.
To preserve clear ideas on the subject of these ​superficial deposits, it is requisite to classify them, not according to a scale of time, which is seldom applicable, but in relation to the predominant agency concerned in their production. Thus we shall have the several principal groups further subdivided as under:—
| 1. Detrital deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | a. Erratic block group. |
| 1. Detrital deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | b. Ossiferous gravel, pebbly clay, sand, &c. |
| 1. Detrital deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | c. Ossiferous caves and breccia. |
| 2. Marine deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | a. Raised from the sea, or, |
| 2. Marine deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | b. Yet in progress. |
| 3. Fluviatile deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | a. Terraces on the valley side. |
| 3. Fluviatile deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | b. Deposits in the valley. |
| 3. Fluviatile deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | c. Ossiferous caves and breccia. |
| 4. Lacustrine deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | a. completed in former times. |
| 4. Lacustrine deposits. | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | a. Raised from the sea, or, |
"Detrital Deposits." "Drift." 'Diluvium." "Boulder Formation."
Since the date of the 'Reliquiæ Diluvianæ' and 'Ossemens Fossiles' many geologists have been accustomed to refer to a particular era and a violent agency the destruction of many land animals which lived with elephants and mastodons on the surface of Europe: the era was supposed to be the termination of a long post tertiary period in which these animals lived;—the agency something of the nature of a cataclysm, and very extensive, if not universal. Their opinions were founded principally on the superficiality of situation, confused aggregation, and similarity of organic contents, in the gravel, sands, and clays which constituted the deposits, and in many instances appeared to have been moved enormous distances across valleys and seas or over elevated ranges of ground. These deposits were supposed to have happened on the dried and elevated land, because of the occasional abundance of bones of land animals in them; yet they appeared to be due to the action of large bodies of water: and the notion commonly entertained was, that the sea had been, by some violence of nature, thrown over the land, so as to destroy, at one definite epoch, over large tracts of the globe, ​whole races of the existing mammalia, and greatly modify the physical aspect of our planet.
Fresh discoveries showed, that the diluvial accumulations contained a great variety of deposits accumulated under different circumstances, by water moving in different directions and with various degrees of force: the remains of elephants, mastodons, &c., were found, though rarely, in really tertiary strata, both marine and freshwater; it was further observed, that the diluvial masses were totally absent from some districts, and in others appeared to have gone in various directions from a particular group or range of mountains. Influenced by these considerations and the growing importance of the study of modern causes in action, some of the most eminent geologists of England dissented totally from the views of Dr. Buckland, and declared, from the chair of the Geological Society, their conviction that the diluvial deposits did not belong to the effects of one general flood, and were not really distinguishable in origin, on the one hand, from the tertiary; and, on the other, from the modern effects of the sea, the rivers, and the land.
Perhaps we may be allowed to regret both that the "diluvial" theory, as it was termed, was at first so confidently embraced, and extended to so many phenomena, and that afterwards it was formally abandoned, without that full and patient discussion of the reasons which should ever precede the rejection as well as the adoption of generalisations in science. In one point of view, the sudden rise and decline in popularity of this doctrine may be very advantageous to geology, since many persons who were so inconsiderate as to attach much importance to the seeming conformity of the "diluvial catastrophe" with the Scriptural deluge, may learn from this example the danger of confounding the really independent bases of religious and natural truth; the former resting on moral evidence and the nature of man, the latter on physical facts and the sure laws of nature. Both are true and cannot disagree, but we ​must know them both well before we attempt the serious task of determining the manner of their union.
a.—Erratic Block Group.
In the British islands, very considerable tracts of country have been traversed since the land had its present general aspect of hill and dale, and was inhabited by large quadrupeds, by currents of water due to some unknown cause, which transported rock masses with so great a degree of force, to points so elevated, in such directions, and at such distances, that we cannot avoid feeling extreme astonishment, and look around in disappointment on the physical processes now at work on the earth, for any thing similar. But it is only in particular tracts that the magnitude of the transported rocks is such as to deserve the title of erratic blocks; and, among several examples, we know of none which more strikingly exemplify the phenomena, as the dispersion of granite, slate, porphyry, &c. from the vicinity of the English lakes, because the nature of the rocks and the limited extent of that region render the observations and inferences more precise than when reference is made to the Grampians, Lammermuirs, or mountains of Wales.
Many, perhaps most, of the Cumbrian mountains have yielded detritus to the diluvial currents (a term we here employ for its convenience, without wishing to convey any hypothetical notion beyond that of the force of their movement); but certain of them contain rocks so remarkable, that wherever fragments of these are seen in the gravelly deposits of the neighbouring regions, an experienced eye may at once refer the pebbles to their parent site. Such are the granites of Ravenglass and Devock lake: in a still higher degree the porphyritic granite of Shap fell, the sienitic and hypersthenic rocks of Carrock fell, the amygdaloidal slaty rocks of Borrowdale, some kinds of slaty rocks full of fragments about Grasmere, certain felspathic rocks at the base of Helvellyn. It appears to be certain that, in the dispersion of boulders of these rocks, the present ​physical configuration of the neighbouring regions had great influence: they are found to descend from the Cumbrian mountains northward in the Vale of Eden to Carlisle, eastward to the foot of the Penine chain, southward by the Lune and the Kent to the narrow tract between Bolland Forest and the bay of Morecambe; and from the vicinity of Lancaster they are traced at intervals through the comparatively low country of Preston and Manchester, lying between the sea and the Yorkshire and Derbyshire hills, to the valley of the Trent, the plains of Cheshire and Staffordshire, and the vale of the Severn, where they occur of great magnitude. It thus appears, that the Penine chain, ranging north and south, acted as a great natural dam, limiting the eastward distribution of the blocks; but at Stainmoor, directly east of Shap fells, a comparatively low part of the chain (1400 feet above the sea), granite from Shap fell, which is about 1 500 feet, as well as sienitic rocks from Carrock fell, which is 2200 feet, and red conglomeritic masses from Kirby Stephen, only 500 feet above the sea, have been drifted over the ridge.
* 1. Shap fells, whence the granite blocks have been drifted to
* 2. Orton Scar, a range of limestone hills, and from these have passed
* 3. The Vale of Eden, in new red sandstone.
* 4. Stainrnoor Forest, across which, in the lowest part of the range of the Penine chain of hills, the boulders have gone to
* 5. The Vale of York, &c.
* 6. The Oolitic moorlands.
This great barrier passed, the blocks are scattered from Stainmoor, as from a new centre, to Darlington, Redcar, Stokesley, Osmotherly, Thirsk, and the whole front of the Hambleton hills; they have gone down the whole length of the vale of York, and by the base of the chalk wolds to the Humber. But the barrier of oolite and chalk has been in places surmounted, and the ​Shap fell granite lies on the moors near Lastingham, and near Scarborough, and on the wolds near Flamborough, Middleton, &c.
The Penine chain ends abruptly on the north against Brampton, Hartley Burn, Hexham, &c.; and a great depression is formed on the line of the 90 fathom dyke and the vale of the Tyne. Along this depression, and far down to the mouth of the Tyne, the Cumbrian detritus is found, though no streams now flowing there have any connection with the mountains from which the materials came.
The large quantity of detritus from the Cumbrian mountains, which has been drifted to the south, on the western side of the high mountain border of Yorkshire and Derbyshire, has gone across the drainage of the Lune (Lancaster), Wyre, (Garstang), Ribble (Preston), Mersey (Manchester), Weaver (Northwich), into and beyond the drainage of the Trent, the Dee, and the Severn (Bridgnorth). Not in any instance have they overstepped to the east the mountain barrier previously noticed; but they lie up against it in enormous quantity, and in the most inextricable confusion, not to be explained by any thing like the action of the sea on its coasts, even during the most violent storms.
In and under Barr Beacon, is a mighty mass of drifted quartz gravel, and sand, with fragments of limestone, trap, and coal sandstone rocks from Dudley, Rowley, &c.; but I found no distinct proofs of Cumbrian rocks,—not a bit of granite, and no bones. This seems to be analogous to the great drifted mass of gravel, coal, and sand at Durham, which has followed the drainage of the Wear.
The distribution of pebbles of quartz rock from Bromsgrove Lickey to the north and east, even to the valley of the Thames, and along the hills which border it, is well known from Dr. Buckland's description, and certainly it is one of the most striking examples of the effect of ancient currents; but it appears totally independent of the "drift" from Cumberland. ​
Let us then return to the Cumbrian mountains, and mark the nature of the forces indicated by the superficial area and the geographical features of the region covered by the erratic detritus. It is remarkable, in the first place, that the detritus in question has been transported chiefly to the south and east, slightly to the north, and hardly at all to the west. The same thing is true for the greater part of the diluvial accumulations in England. In the southward direction, the moving forces were sufficient to conquer such obstacles as the bay of Morecambe, and all the undulated and hilly region between the mountain border of Yorkshire and Derbyshire, and the Irish Sea, but not to pass that mountain boundary; and of such continuity, as to be recognised as far at least as Bridgnorth, 130 miles and more from their origin. In an eastward direction, the boulders have crossed the bold limestone ridges of Orton and the deep and broad vale of the Eden; from this they have been raised over the Penine chain of mountainous land, but only at one and that the easiest pass, which, however, is 900 feet above the Eden. Could we venture to assume, in this case, that one long slope of surface formerly continued from Shap fells, and Carrock fell, to Stainmoor, the arrival of the blocks on the latter point might be explained: but the hypothesis is wholly gratuitous; for the rocks of the Penine chain, of which Stainmoor is a part, must have been elevated above the strata of what is now the vale of Eden, even at so ancient a period as the deposition of the new red sandstone; since the Penine fault, to which that elevation is due, was anterior to all, or nearly all, the red sandstone formation; and there is no proof, nor reason to imagine, that any strata were superimposed on that red sandstone, so as to fill up in any degree the ancient vale of the Eden.
Whatever hypothesis be proposed for the transit of the blocks from Shap to Stainmoor, must include the consideration of this original difference of level on the line of the movement. Once on the summit of the pass ​of Stainmoor, the natural course of the vales of Tees and Greta may account for the directions at first taken by the boulders to Darlington; and the plains of Cleveland, and the vales of Mowbray and York, easily conduct us to the Humber. But still the same kind of difficulty as that presented by Stainmoor meets us at the foot of the Hambleton hills and the wolds of Yorkshire, over which high and continuous ranges, the boulders have been lifted from the vale of York, which spreads wide and far, several hundred feet below, and drifted onward till they reach the sea, 100 and more miles from their parent rocks.
On the line of these hills there is no great dislocation of strata: their elevation was probably effected by a general upward movement of the whole area of the eastern side of England, affecting equally the chalk wolds, oolitic hills, and red sandstone vale. As, therefore, it by no means follows in this case that such distinctions of level were aboriginal (as in the instance of Stainmoor and the vale of Eden), it may be imagined, that from the Penine ridge to the German Ocean, one long slope permitted descending streams to transport the detritus; and that to the same or subsequent watery force we must ascribe the production of the inequalities which render the transport of the boulders, in the directions they once took, impossible now, without extraordinary dynamical means.
But, granting this, we shall still advance but little in the explanation of the phenomena. For if it be admitted that currents flowing from the Penine ridge toward the east could remove all the mass of materials, thus imagined to rest on the carboniferous rocks, why have they left on the summits of the hills, and on the lower ground of this very region, plenty of the blocks of granite, which, by the hypothesis, should have been swept away over the unwasted surface? Dismissing, then, for the present, the notion that drainage waters, under any possible condition of levels of the dry land, could disperse these erratic boulders, let us inquire ​under what circumstances they might be moved by the waters of the ocean.
Either we may suppose the waters to be thrown in a body over the land, so as to conquer by their violence and volume certain inequalities of the surface, and to cause particular local currents depending on the resistance offered by the physical configuration of different districts; or we may imagine alterations in the relative level of land and water, in the whole region where the detritus is spread, of sufficient amount to permit the transfer of heavy bodies by oceanic currents over surfaces which subsequently (at once or in succession) became dry land. This latter supposition admits of many gentle or many violent upward movements of the land round a vertical axis; and in this instance the axis may be imagined to pass parallel to the extreme points whereto the detritus has reached, viz. Bridgnorth and the mouth of the Humber, or north-east and south-west; and the movement to be upwards in all the region between this and the Cumbrian mountains. The consequence might be, dispersion of gravel, &c. from the primary mountains, in various directions within the semicircle from N.E. to S.W.; and it is entirely within this range that all the Cumbrian detritus is really located. To determine whether the upward movements assumed were gentle or violent, we must look to the deposits of boulders and gravel which have resulted; and as the leading facts which they exhibit are undoubtedly the heterogeneous admixture of substances of different magnitude and density, the absence of parallel and continuous stratification, and the frequency of contorted and inexplicably jumbled masses, we cannot hesitate to pronounce in favour of sudden and violent movements of incomparably greater energy than those by which most of the old conglomerate rocks were formed.
Geologists to whom this reasoning is not satisfactory may take as a basis of deduction the other speculation, that the ocean has been violently thrown over the land. ​This is impossible as an ordinary occurrence. No ordinary combination of circumstances could much augment the fluctuations of the ocean beyond their present amount: if the equatorial course of the tide were free, and the impulses of the sun and moon could be supposed to conspire in augmenting the rise, successively, as isochronous applications of small forces will enlarge the vibrations of a suspended bar, this would not correspond either in magnitude or violence to the phenomena which require explanation. It is impossible, therefore, to assign a physical cause for such a mighty overflow of the ocean, except we suppose the earth's figure to be changed; its axis displaced, and thus the sea moved in mass, or its crust broken, and thus new basins opened to the waters. The displacement of the earth's axis cannot be assumed, on satisfactory grounds, as a thing within the range of probability; for the earth is a figure of equilibrium, and therefore its axis is fixed, as far as any ordinary tendencies in the mass itself are concerned; and neither comets nor planetary attractions are thought to be influential for such an object. We are, therefore, reduced to the supposition of violent disruption of the crust of the earth, if we wish to explain diluvial phenomena by one or many transient overflows of the sea.
Whether, therefore, we suppose the dry land to have been covered by boulders through an inroad of the elevated sea, or the unequal bed of the sea to have been raised, in either case it is necessary to admit violent fracture of the earth's crust, and on either view we may venture to generalise the phenomena connected with the dispersion of boulders from the Grampians, Scandinavian ranges, Cumbrian rocks, and primary strata of the north of Ireland, in one point of view. For the same speculation of a rise of land parallel to an eastward or north-eastward line, if it will account for the phenomena in the north of England, will also explain those of the other localities, if the axis be taken far enough south, and the area moved be supposed to ​extend at least as far as the Irish, Scotch, and Scandinavian coasts; and a great oceanic current from the north or north-west, if possible and applicable in the case of Shap and Stainmoor, must be supposed to have left traces of its power on other mountain ranges. It is unnecessary to extend these reflections arising from the phenomena of the dispersion of Cumbrian rocks farther than to observe, that the line followed by the blocks southward from Shap through Lancashire, and northward to Carlisle, is in a great depression parallel to the fault of the Penine chain; and that the depression on Stainmoor, and that farther north near Brampton, by which similar blocks have gone eastward, are occasioned by cross faults which break the continuity of that same chain. These circumstances are obviously important.
The most prevalent direction in which the blocks have been transported in the British isles, is from north to south; but, in general, the natural configuration of the ground appears to have had considerable influence in determining many minor currents. The same conclusion, of the influence exercised by the local configuration of land, results from the laborious examination of the phenomena of the dispersed blocks of the rocks of the Alps. The existing valleys are the lines by which the fragments of the mountains have been drifted away to the lower grounds of France, the Pays de Vaud, Switzerland, the great vale of the Danube, and the plains of Lombardy. Not that the rock masses are carried along the course of the actual stream, or even confined to the course of the valley; for mountains lying in the main direction of the valley, through 3000 or 4000 feet high, are as thickly, and even, in the case of the Saleve and Mont Sion near Geneva, more thickly, covered than the hollow of the Arve, or the banks or bed of the Rhine and Leman Lake. It appears, therefore, that some great violence of water acting along the line, but not limited to the level, of the present drainage, has brought the blocks from the western Alps, by ​the valleys of the Isere and the Durance, to the plains of the Rhone: thus have the rocks wasted from around Mont Blanc, and the Col di Balme been strewn over the valley and along the hilly borders of the Rhone, even to the height of some thousand feet on the Jura; near Soleure, the same range of mountains bears the spoils of the Bernese Oberland, swept down by the valley of the Aar, the Claris boulders have gone to Zurich, and those of the Grisons have descended the valley of the Rhine. But, after thus falling to the great Swiss tertiary basins of Geneva, and the valley of the Aar, the blocks have crossed those hollows, and been driven up the opposite slopes of the Jura to a level 2000 feet higher. De Luc (Mém. de la Soc. d'Hist. Nat. de Génève) notices the origin of other rocks besides the granites dispersed in the basin of Geneva, and they support the same conclusion of the decided influence exercised by the present configuration of the country in modifying the direction of diluvial currents.
This influence is, however, in other cases, less sensible. For example, the zircon sienites, porphyries, and transition limestones of Sweden and Norway, have been transported southwards over the country of Scania and across the Baltic, and scattered over the sandy plains of Westphalia, Hanover, Holstein, Zealand, Mecklenburg, Brandenburg, Pomerania, Prussia, and part of Poland between Warsaw and Grodno. Thus, from the Ems and theWeser to the Niemen and the Dwina (and even to the Neva), the country is covered with ruins of the Scandinavian rocks brought across the sea, and carried toward the Carpathians, and the Bohemian and Westphalian mountains, contrary to the natural currents of drainage. De Luc and Brongniart have given many details concerning these remarkable boulders, which appear not equally spread over the large tracts of country mentioned, but assembled in groups in particular situations. These groups are often elliptical in form; the major axis of the figure pointing north and south, or toward the Baltic Sea, across which they have been transported. ​Bruckner mentions a trainée of blocks north of Mecklenburg Strelitz, which runs from N.N.W. to S.S.E. They are said to be in general more abundant on the elevations than in lower ground, the largest masses being nearest the summits, as if the lighter gravel and sand had been removed from them.
De Luc observed, in Lower Saxony, circular ridges of hills with a single outlet from these natural amphitheatres; and on the inner faces of the hills abundance of granite, porphyry, &c. There can be no doubt that the great masses of granite, porphyry, transition limestone, &c. scattered over the north of Germany, have been derived from the Scandinavian mountains, because the limestones contain organic fossils peculiar to the transition rocks of Sweden; the porphyries and granites are equally identified by their mineral characters; and the distribution of the groups of blocks on the south of the Baltic, as well as the traces of their passage across Scania, completely agree with this conclusion. The era when these blocks were drifted across the Baltic, though modern when compared even with tertiary strata, is yet very remote, for they lie under the ancient peat mosses of East Friesland; and there appears reason to think that more than one such migration of erratic blocks has accompanied the upward movements of the Scandinavian primary regions. "Almost the whole surface of North America, as far as examined, may be said to be covered with an investment of earth, pebbles, and boulders, obviously of diluvial origin. The thickness of this deposit varies, though its average depth may be said to be from ten to twenty feet. All that low and level tract described as the Atlantic plain, and also the lower sections of the great valley of the Mississippi, appear to be the districts where it conceals the underlying strata to the greatest depth."—"The boulders may almost invariably be traced to formations which lie at some miles' distance, to the north-west and north. This distribution of the diluvium from the north and north-west is not confined to the rivers whose ​valleys run in these directions, but belongs, it is believed, to at least all the middle and northern latitudes of the continent. It is seen west of the Alleghanies, throughout the regions of the Ohio and Mississippi, as well as extensively over the Atlantic slope and the tertiary Atlantic plain. Bigsby, and the travellers to the north, have already shown it to prevail in the latitudes north of the United States."
These and many other cases demonstrate—
1. That the course of the blocks from their original site has been influenced by the present configuration of the country; because they are accumulated in greatest abundance in the lower regions of the earth, and have often gone by the line (though not limited to the level) of the great drainage hollows of the surface.
2. The mechanical forces which transported these boulders must have operated under totally different conditions from these which determine the course of the actual streams; because the boulders have crossed great vales and seas, and ascended ridges, quite contrary to the course of existing drainage.
3. It is impossible to comprehend the phenomenon as one capable of being produced by the watery agencies now at work in nature, except under different dynamical conditions; such as a disturbance of the oceanic level to an enormous degree, hardly conceivable except as the result of a general change of the figure of the globe, produced by a displacement of its axis of movement; an incredible and irregular alteration of dimensions; or a series of elevator and depressing movements operating in certain directions. Ignorant as we are of the extent and character of diluvial phenomena in all the southern zones of the world, it is desirable to avoid a decision on the much controverted origin of the erratic blocks, especially as some of the proposed solutions are mechanically absurd. One of the most ingenious, and perhaps least hypothetical, of the modern notions on the subject, is, ​that the great blocks of the Alps and Scandinavia were floated away on icebergs, and so dropped on the sea bed or on the temporarily submerged land. That icebergs are detached from the land with stones on their surface is known to northern navigators; it is a phenomenon well understood in the Gulf of Bothnia; and, to an imaginative mind, the mer de glace, with its border of moraine, might seem a natural component of such a glacier current as that to which the Salève, the Jura, and the borders of the Lake of Geneva are supposed in this hypothesis to owe their accumulated blocks. It is thought to be a plausible argument in favour of this speculation, that the blocks of granite, porphyry, limestone, &c. are grouped together in distinct patches according to their local origin, both in the vicinity of the Alps and on the plains of northern Germany.
Icebergs are merely the broken-off ends of glaciers, which descend to the sea, or the detached fragments of icy cliffs generated on the coasts of circum-polar regions. When liberated they are carried by oceanic currents through various and often great distances, till, melted, overthrown, or stranded, they yield up the stony masses, which glaciers had brought down, or shore ice had raised up, and thus encumber the sea bed with the spoils of distant lands. When the antarctic expedition had reached 78 south latitude, the vessels were stopped by a barrier of ice, from 100 to 180 feet in height, and 300 miles in extent from east to west; beyond these cliffs of ice, a range of lofty mountains was visible about 60 miles distant, the westernmost of which appeared to be 12,000 feet high. From the face of these ice-cliffs masses were constantly breaking off, and floating northward, bearing with them fragments of rock, probably derived from the mountains from which the glaciers appeared to descend. In the lat. of 66° and 67°, at a distance of 700 miles from the glacier, the ice formed a floating barrier, through which the ships could with ​difficulty force their way. Over the intermediate area the ice-bergs would be constantly strewing masses of rock and detritus, particularly at their northern limit, where they would probably form mounds resembling terminal glacial moraines ! As the stranding of icebergs would happen on sandbanks and shoals, we might expect accumulations from this cause to be more prevalent on hill tops, and along the sides of broad vales, than in the depths of valleys; and such is well known to be the fact in many examples of erratic blocks.
Thus, in describing the vast extent of detrital deposits on the broad surface of European Russia, in fact, from the German Ocean on the west to the White Sea on the east, Murchison expressly marks the discontinuity of the erratic masses, and their greater frequency on plateaux, and especially on the southern sides of these plateaux. Accumulations of like nature form hills (escars in Ireland, osars in Scandinavia, barfs in England), in which often some peculiar disarrangements may be remarked in the accumulated detritus, not unlike that in true 'moraine.'
A difficulty which occurs in receiving glaciers on land and icebergs at sea as a full explanation of the phenomenon of transported blocks is this:—Two cases have been pointed out by the author of this treatise, where, beyond all doubt, portions of remarkable rocks have been lifted by the transporting force to much higher levels on neighbouring hills, and under conditions which leave no room for supposition that the difference of land has been occasioned by unequal movement of ground since the dispersion of the blocks. In one case (Craven) large masses of lower palaeozoic slaty rocks are lifted up in great numbers on to the limestone which lies level on this very slate. In another (Stainmoor), a red conglomerate, of very peculiar character and local ​origin, has been raised over the narrow pass in the hills above, from a height of 500 to one exceeding 1,400 feet. For these and many other cases mentioned by other authors, Mr. Darwin offers the ingenious explanation afforded by shore-ice, formed during a general and continual subsidence of the land over large areas. By this combination, the boulders on the shore might be frozen and refrozen at levels necessarily higher and higher, as compared with the land, drifted and redrifted in floating ice, and subject to more or less of rolling and attrition, till in small numbers, in limited tracts, and under peculiar geographical conditions, they might assume the paradoxical situations for which mere sea currents cannot account.
The supposition that erratic blocks have been transported by floating ice, leads to an admission that much of the surface of the northern circumpolar regions, which is now dry land, was under a sea periodically chilled by abundance of ice, if not placed permanently on lower isothermal bands than at present. It is an equally clear inference that the lands from which the ice-rafts started—for example, the Scandinavian and British Highlands—were extensively overspread by glaciers. But they were, by the hypothesis, at a lower level; and it becomes necessary to assign a reason for their greater cold under a condition which in the given examples is actually favourable to augmented temperature. As things are, if our British mountains were lowered a few hundred feet, their summits would grow warmer, and there would be even less chance than at present for the production of glaciers on them. By the same depression the Scandinavian glaciers would be contracted, The cause is probably given correctly by Mr. Hopkins, and is simply the displacement of the northward current of warmed water ('gulf stream'), which, bathing the shores of Britain and Norway, exalts their temperature at present about 15° above that of the corresponding latitude on the east coast of North America. This gulf ​stream, or rather the general flow of warmed water to the north, is variable by slight causes in the present system of nature, and may be admitted to be displaceable by a great disturbance of the sea-bed. Such disturbance must have happened. But further, the northward warm flow of the sea is balanced by a return cold current. It is conceivable that this return of cold water may have passed through the area where erratic blocks occur in Europe, and thus we should have abundantly the elements of cold required for glaciers on the land which stood above the waves in Britain and Scandinavia, It is no small confirmation of this view that we find in the gravel and clay, associated with erratic blocks, and clearly forming the sea-bed of their era, shells which, upon the whole, indicate an arctic character of the marine fauna of the period. It is further important that we find in the valleys of Scandinavia, and the Irish Cumbrian and Grampian Highlands, marks of radiating glaciers, rocks worn and striated for hundreds of feet below the summits; in fact, almost or quite down to the actual sea level, and much below the probable level of the ancient sea which floated the icebergs. Spitzbergen, according to Dr. Martins, gives us at present examples of glaciers which pass to some distance from land, and to some depth below the sea.
Striation and broader grooving of hard rocks on the line of glacier movement are found extensively round the Scandinavian mountains. But it occurs also in low ground in Russia, as on Lake Onega, where the configuration of land to the north forbids the belief that glaciers could be formed. From these and other instances, we must admit with Murchison, that ice dragged on the stony bed of the sea might become a powerful agent. for scratching the rocks, the stones which covered them being also scratched, a circumstance which has caught the attention of Mr. Miller, in his examination of the boulder clay. It does not occur on sea beaches, ​in the channels of rough streams, or in ordinary gravel beds.
The former boundaries of the glacial sea may be in some degree conjectured by the distribution of the northern drift, for it must have extended beyond the area of that drift. The depth to which the mountain regions from which the most abundant erratics have been distributed were sunk, may be in some degree conjectured; the Grampian, Cumbrian, and Cambrian Highlands, may, perhaps, have been 1500 feet, and the Alps, perhaps, 3000 feet lower. Under these conditions all the lower grounds of northern Europe would be submerged; the masses of mountainous land would appear above the waves, covered with snow, and surrounded by icy floods.
In this broad ocean, cold sea currents flowed most abundantly, though not exclusively, from the north and north-west, and drifted the rocks of Finland and Scandinavia to the plains of Russia and North Germany; the syenites of Criffell to the slopes of Skiddaw, the granites of Shap and Ravenglass to Yorkshire and Staffordshire. Agitations of water, anterior to and coincident with the elevation of the land toward its present height, have disturbed and modified the materials left by the ice-rafts, and mixed them with materials derived from wasting coasts, river floods, and the wearing of the sea-bed. These we shall now consider.
Ossiferous Gravel, Pebbly Clay, Sand, etc.
While some remarkable cases of dispersed boulders have engaged the attention of geologists following in the track of Saussure and De Luc, thousands of examples offered themselves of accumulations similarly at variance with the existing agencies of water; but they were never accurately studied till they acquired a new interest from the discussions of De Luc, and the splendid researches of Cuvier into the bones of quadrupeds which ​lie abundantly in these deposits. Large portions of England, Wales, Scotland, and Ireland, are covered by irregular aggregations of gravelly sands and pebbly clays, locally stored with the bones of various land quadrupeds, which appear to have lived not far from the spots where they now occur buried. The parts where they occur were therefore dry land, or, at least, not far removed from the native haunts of the animals.
The pebbles constitute the essential and characteristic part of these deposits, and enable the geologist to decide, in some cases very positively, as to the direction in which they have been drifted. Generally, in all the north of England, the diluvial gravel has been transported by the same routes or the same points of origin as the boulders; but there is some variety in this respect worthy of notice. On the eastern side of the island, from the Tyne to the Humber, the gravelly deposits appear partly of local and partly of distant origin. On the Yorkshire coast, local gravel, derived from the chalk wolds or oolitic moors, lies in very irregular beds, distinct altogether from the clays full of pebbles brought from the Cumbrian and Penine mountains; at Bridlington, local chalk and flint gravel lies over the other diluvium, and at Hessle, on the Humber, similar local gravel lies under it.
It might be proper, in these cases, to confine the term diluvium to that portion of the gravelly masses which, by the abundance of the fragments from very distant parts, requires the supposition of extraordinary circumstances for its accumulation. It is not solely, nor, perhaps, even principally, in this proper diluvium, that the bones of elephants, hippopotami, horses, deer, &c. occur; they seem, on the contrary, to be rather more plentiful in the local gravel deposits. Cases, however, occur, as at Brandsburton, and at Middleton on the Wolds, near Beverley, of elephantine and other remains in the midst of erratic gravel derived from great distances.
The most singular circumstance attending the accumulation of the proper diluvium is the extreme ​confusion, and almost total want of laminar or stratified structure, in its mass: pebbles, and fragments of rock, of all sizes, of different nature, and from different regions, lie mixed indiscriminately in clay many yards in thickness; which seems clearly to prove that the whole was rapidly accumulated, and that the particles had not time to be arranged according to magnitude or specific gravity, but were heaped confusedly together by a force of extraordinary intensity and short duration.
Local Gravel. per Diluvium. Similar explanations seem applicable to the pebbly clays of Lincolnshire, Huntingdonshire, and Northamptonshire, &c.; and to the whole track of the diluvium from the lake mountains through Lancashire. Cheshire, Staffordshire, &c.
Many parts of England are almost totally free from the accumulation of proper diluvium,—as the Yorkshire coal-field, the Wealden denudation, large tracts in North Wales, the vicinity of Bath, &c. But these districts contain abundance of local gravel deposits, which sometimes appear to be quite as ancient as the diluvium, and may justly be styled "ancient alluvium;" for their aggregation seems not, in general, to require the supposition of watery agencies flowing in other than the directions of actual streams and inundations. Much of ​the gravel which is collected below the openings of the valleys which descend from the Grampians is of this local character; but that which abounds in the central plains of Ireland, constituting the 'escars' of that country, has been drifted from greater distances, and appears due to more general agency.
Mr. Murchison's examination of the Welsh border appears to show that the gravelly deposits formed from the waste of those districts, and forced down to the great hollow uniting the vales of the Dee and the Severn, were transported, according to the descent of the country, previous to the dispersion of the erratic blocks from Cumberland; and he supposes that, between the mountains of Wales and the oolitic ranges, the vale of the Severn was submerged, and constituted part of a long strait uniting the Irish and Bristol Channels, since the northern zones were inhabited by quadrupeds. The abundance of shelly deposits mixed with and lying under the detrital accumulation of Cheshire, Worcestershire, &c. appears to justify this view.
It is, therefore, by no means a simple problem which the superficial gravel deposits of even a limited district offer to the reasoning geologist. Gravel is not necessarily of diluvial origin; does not necessarily imply the action of violent forces, or currents moving in directions which could only be rendered possible by a great change of the relative level of land and water. We must, in all cases, distinguish between the local and general agencies which, separately or in combination, effected the transfer of the gravel. The pebbles on the plain of Crau at the mouth of the Rhone, and those vast heaps brought from the Alps of Dauphiné by the Isère and the Durance, have one local origin; almost every valley of the Alps and the Grampians has served for the passage of a peculiar suite of broken rocks; only at one point of the Penine chain of England have the Cumbrian rocks been drifted to the drainage of the Humber. Geographical circumstances appear to have been more important in determining the distribution of gravel, than of erratic blocks, even though we assume the effects in all cases to ​have been produced by the same agencies. Before any particular masses of sand, gravel, or pebbly clays can be pronounced to be of diluvial origin, and adduced in evidence on the question as to the origin and operation of violent waters, it is indispensably necessary to show that, under the present configuration of the surface, with ordinary measures of local watery forces, the accumulation of such masses is impossible. This can be shown, if the component pebbles of the presumed diluvium can be referred precisely to the situations whence they were dislodged, and these situations are separated by natural obstacles from any part of the drainage hollows connected with the locality where the gravel is found. Some gravel is, or may be, of local origin, the effect of existing streams, or of waters which may be conceived to have formerly flowed according to the present slopes and physical features of the country; and descriptions of gravel deposits are almost useless, in which the question of local or distant origin of the masses is not examined.
Supposing this point settled, and the deposits to possess the characters of diluvial accumulation, the next thing is to determine how far similar deposits are traceable in the neighbouring districts, and toward the presumed origin of the fragmentary masses, so as to determine the direction really followed by the currents which transported them. The circumstances of the accumulation should be carefully studied. If accompanied by local gravel, does this lie upon, or below, the diluvial masses? for both these cases occur. Is the mass in any respect stratified? Does its composition suddenly vary? Is there oblique lamination of any of its (sandy) parts? Are large and small, heavy and light, masses indiscriminately mixed? Are the fragments angular, greatly rounded, or flatly elliptical? Are bones of quadrupeds or shells of mollusca found in the mass, or lying in marly beds above, below, or inclosed? The problems thus suggested are of great importance toward a correct view of the origin of the diluvial accumulations, and the contemporaneous races of organic beings. ​
Ossiferous Caves, and Fissures in the Rocks.
The land animals mentioned in the last section appear to have been, for a considerable geological period, inhabitants of the countries where their remains are buried in the gravel; for their bones are also found in caves, and fissures of the rocks, under circumstances generally indicative, and often demonstrative, of their habitual existence in the cave, or the vicinity of it. Here, buried in mud, or covered by calcareous deposits, inclosed and perfectly preserved, lie the separated bones of many kinds of extinct quadrupeds, young and old,—entire, broken as by falling into a pit,—worn by currents of water, or gnawed by ravenous beasts; but often perfectly recognisable, and capable of being rigorously compared with living races of mammalia.
The result is extremely remarkable: instead of a large proportion of the existing species of animals, which, during the early periods of history, if not in later times, might have been expected to fall into fissures, retire into caves, or be dragged by wolves to their dens; we find the greater number of bones to belong to elephants, large feline animals, the rhinoceros, hippopotamus, elk, hyaena, indiscriminately entombed with oxen, deer, and many smaller animals. The contents of the caves have a considerable general analogy in a given country, as England; but they exhibit some characteristic differences, when different districts, as Franconia and Yorkshire, or Narbonne, are compared. These local differences are important additions to the evidence afforded by the state of inhumation and conservation of the bones, in favour of the conclusion that the animals found in the caves were really the inhabitants of the neighbourhood. The following general list of the species of mammalia found in alluvial and diluvial deposits may be useful for reference. Man is included in the catalogue, though it appears improbable that the remains of the human race found in the caves of Bize, Belgium, &c. are really of the same date as the elephantine exuviæ in northern climates. (See Desnoyers' Report to the Geol. Society of France.) ​
GENERAL TABLE OF VERTEBRAL REMAINS IN POST-TERTIARY ACCUMULATIONS.
| Name. | Alluvial. | Diluvial. | Breccia. | Caverns of all Periods. | Volcanic Detritus. |
| Man and human construction. | Guadaloupe, Baden, Köstriz, Austria | | Nice, Dalamatia | Bize, Sommières, Rancogne, Ussat, Miallet, Engissoul nr, Liège, Paviland, Mendip, &c. &c. | |
| Elephas primigenius, Blum | | Europe, N. Asia, N. America | | Kirkdale, Mendip, Muggendorf, Zahnlock, Fouvent, &c. | Auvergne |
| priscus, Goldfuss | | Englang, Germany, Prussia | | | |
| Hippopotomaus major, Cuv. | Lancashire | England, France, Germany, Tuscany | | | |
| intermedius | | Dep. Maine et Loire | | | |
| minutus, Cuv. | | Near Bordeaux | | | |
| Rhinoceros tichorinus, Cuv. | | Siberia, England, Germany, France, Italy | Haute Saone | Harz, Küloch, Chockier, Kirkdale, Defbyshire, Preston | |
| leptorhinus, C. | | Tuscany | | | |
| Incisivus, C. | | Eppeilshem | | | |
| Minutus C. | | Moissac, Elgo in Switzerlad near Magdeburg | | pondres? | |
| Asiaticus, Bl. | | | | Chokier | ​ |
| Tapir giganteus, C. | | S. of France, Bavaria, Austria, Eppelsheim. | | | |
| parvus, C. | | Languedoc? | | | |
| ? | | Irawadi R. | | | Auvergne. |
| Mastodon maximus, C. | | N. America, Auvergne, Siberia, Ural. | | | |
| angustidens, C. | | America, Italy, England, Germany, Montpellier. | | | |
| andium, C. | | S. America. | | | |
| Humboldtii, C. | | Chili. | | | |
| minutus, C. | | Saxony. | | | |
| tapiroïdes, C. | | Europe. | | | |
| latidens, Clift | | Irawadi R. | | | |
| elephantoides, Cl. | | Irawadi R. | | | |
| Tetracaulodon mastodondoïdeum, Godman | | Newbury, N. America. | | | |
| Elasmotherium Fischeri, Desm. | | Siberia. | | | |
| Sus priscus, Goldf. | | Scania | | Mendip. | |
| arvernensis | | | | | Auvergne. |
| vulgaris | England, Scania, &c. | | | | |
| Equus caballus | England, France, &c. | Beibecks, Yorkshire | | Lunelvieil, Oreston, Kirkdale, &c. | |
| angustidens, Meyer | | Eppelsheim. | | | |
| small species | | Yorkshire | | Pondres, Argou. | |
| Palæotherium | | | Villefranche, Lauraguais. | | |
| Chœropotamus Pariensis | | | Ditto. | | |
| Felis Spelæa, Goldf. | | Yorkshire, Kent's Hole | | Germany, England. | |
| antiqua | | | | Germany. | |
| large | | | Nice | | |
| small | | | Nice | | |
| | | | | | Auvergne. ​ |
| Name. | Alluvial. | Diluvial. | Breccia. | Caverns of all Periods. | Volcanic Detritus. |
| Hyæna fossilis, Cuv. | | Canstadt, Abeville, &c. | | Germany, France, England. | |
| monspessulana (Christol) | | | | Lunelvieil. | |
| intermedia, M. de Serres | | | | Ditto. | |
| gigantea, Holl | | | | Oreston. | |
| Mustela spelæa? | | | | Gailenreuth. | |
| vulgaris, Lin. | | | | Kirkdale. | |
| martes, Lin. | | | | Gailenreuth. | |
| Talpa Europæa, Lin. | | | | Chockier. | |
| Canis lupoïdes, Cuv. | Yorkshire | Yorkshire | | Kirkdale, Gailenreuth, Chockier. | |
| aureus? Lin. | | | | Gailenreuth. | |
| vulpes, Lin. | | Val d'Arno | | Ditto | |
| familiaris, Lin. | | | | Lunelvieil. | |
| Parisiensis, Cuv. | | | Gibraltar. | | |
| ? | | | Sardinia. | | |
| ? | | | | | Auvergne. |
| giganteus | | Avaray (on the Loire). | | | |
| Ursus spelæus, Bl. | | | General | Very general. | |
| cultridens, Cuv. | | Val d'Arno | | Kent's Hole. | Auvergne. |
| priscus, Goldf. | | | | Gailenreuth, Sundwig, Pondres. | |
| Pittorii, De Saus. | | | | Fauzan, Sundwig. | |
| ? | | | | | Auvergne. |
| Meles vulgaris | | | | In the Muggendorf district, Lunelvieil, Liège. | ​ |
| Gulo spelæus, Goldf. | | | | Gailen, Sundw, Rözenbeck. | |
| Nasua Nicaensis | | | Nice. | | |
| Talpa Europea, Lin. | | Chockier. | | | |
| Vespertilio murinus? Lin. | | | Sardinia | Gailenreuth. | |
| Sorex araneus? Lin. | | | | Gailenreuth. | |
| Cervus euryceros | Yorkshire, Ireland, Isle of Man | Essex, Rhine Valley, Paris, Italy | | Kent's Hole. | |
| tarandus priscus | Scania | Rhine Valley, Lund, Griesswald | | Breuque. | |
| (elaphus) primordialis, Cuv. | England | England, Sweden, France, Rhine Valley, &c. | | Very generally, Germany, Liège, England. | |
| (dama) Sömmeringii, Cuv. | | Sommethal | Gibraltar, Cette, Antibes. | | |
| alces, Lin. | Scania, Cleves, &c. | | | | |
| capreolus, Lin. | Scania, in peat, Dep. de la Somme | | | Argou | Some species of cervus in Auvergne. |
| ? | | | | Bize. | |
| Reboulii | | | | Bize, Argou. | |
| 3 species | | | Nice, Pisa, Gibraltar | Some cervi in Kirkdale Cave. | |
| giganteus | | Albeville. | | | |
| Bos urus priscus | Scania | Yorkshire, Siberia, Rhine Valley, N. America | | Kirkdale, Mendip, Liège, Bize, &c. | |
| fossilis | | | Gibraltar. | | |
| moschatus, Lin. | | On the Lena R. | | | |
| Americanus, Lin. | | Ohio. | | | |
| Arni, Lin. | | Siberia. | | | |
| Capra ovis | Yorkshire | | Sardinia | Gailenreuth. | ​ |
| Name. | Alluvial. | Diluvial. | Breccia. | Caverns of all Periods. | Volcanic Detritus. |
| Capra ammon | | | Nice. | | |
| Antilope | | | Nice. | | |
| Mericotherium | | Siberia | | Montpellier, Villefrance, Lauraguais. | |
| Trogontherium cuvieri | | Sea of Azof. | | | |
| Lepus timidus | | | Gibraltar | Chockier, Liège, Sundwig, Kirkdale. | |
| cunniculus | | | Gibraltar, Cette, Pisa | Kirkdale. | |
| Lagomys sardus | | | Corsica, Sardinia. | | |
| corsicanus | | | Corsica. | | |
| Castor | Dep. de la Somme, Newbury, Berkshire. | | | | |
| Arvicola | | | Corsica, &c. | Gailenreuth. | |
| | | | | Ditto. | |
| Hypudæus amphibius | | | Corsica, Sardinia, Cette | Kirkdale, Chockier. | |
| arvalis, Pallas | | | | Kirkdale. | |
| œconomus, Pall. | | | | Kirkdale. | |
| Mus musculus, Lin. | | | | Lunelvieil. | |
| sylvaticus, Lin. | | | | Lunelvieil, Chockier. | |
| rattus, Lin. | | | Sardinia, Gilbratar | Chockier, Kirkdale. | |
| terrestris, Lin. | | | Corsica. | | ​ |
| Porcupine | | Val d'Arno. | | | |
| Osteopora platycephalus, Harlan | | Delaware. | | | |
| Megatherium australe, Okes | | Buenos Ayres, Lima, Paraguay, Darmstadt | | Francisco River in Brazil. | |
| Megalonix boreale, Okes | | | | Virginia, Brazil. | |
| Manis gigantea, Cuv. | | Avaray, near Orleans. | | | |
| Dasyurus | | | Australia. | | |
| Hypsiprymnus | | | Ditto. | | |
| Phascolomys | | | Ditto. | | |
| Halmaturus | | | Ditto. | | |
| Gryphus antiquitatis | | | Gibraltar. | | |
| Motacilla, Lin. | | | Cette. | | |
| Corvus | | | | Kirkdale. | |
| Alauda | | | | Ditto. | |
| Phasianus gallus? | | | | Lunelvieil. | |
| Gallinacea | | | | Pondres. | |
| Columba | | | | Kirkdale. | |
| Anas (sponsor?) | | | | Kirkdale. | |
| 4 undetermined species | | | | Chockier. | |
| 7 species | | | Sardinia. | | |
| Ardea | | Yorkshire. | | | |
The accounts of fossil reptiles in terrestrial accumulations are very indefinite. Belænæ and mondontes occur in the Forth valley. A variety of land and freshwater mollusca and conchifera, all of existing species, lie in the breccias of Nice, the caves of Bize, Pondres, Villefranche Lauraguais, and in the ossiferous marks and gravel beds of Yorkshire.
The origin of the caves and fissures is obscure, yet the following facts seem to favour the opinion that they owe their formation partly to disturbing movements, and partly to the solvent power of water.
It is a remarkable and general fact, that the ossiferous caves and fissures are situated almost exclusively in limestone, not only in England, but in France, Belgium, Westphalia, Franconia, Wurtemburg, along the Mediterranean coasts, in North America, in Australia. This is, however, not at all peculiar to ossiferous caves, for it is a rare thing to meet with considerable cavities underground in any other rock than limestone.
It does not appear that these cavities are specially abundant in districts where subterranean movements have been most powerful or numerous; hardly one cave in the North of England can thus be accounted for; but it is certain that, in two districts of the same calcareous formation, caves may abound in the thick and massive rocks, but be unknown in those where thinner layers are associated with sandstones and shales. This is remarkably the case with the carboniferous limestone of Yorkshire and Derbyshire: where several hundred feet of "Scar" limestone exist in one thick mass, caves abound, as at Matlock, Castleton, Buxton, Yorda's Cave, Wethercote Cave near Ingleton, Gowden Pot Hole in Nidderdale, Dunald Mill Hole near Lancaster, &c.—but not a single cave is known among the thinner and more varied "Yoredale Rocks."
Kirkdale Cave is in a very thick part of the coralline oolite, and calcareous grit; the Franconian and other German caves are also in thick rocks of limestone.
It appears remarkable, that so large a proportion of the known caves are situated near, and open on the sides of, existing valleys, though often much above their actual level; along some vast bodies of water are now running, and daily enlarging the passage (Peak Cavern, great cavern in Nidderdale); and from the mud mixed with the bones in even the driest repositories, from the decomposition and wearing of the surface of the bones, the stalagmitic ​floors, stalactitical canopies, and other signs, there is no room to doubt that in all the ossiferous and common caves the solvent and mechanical powers of water have been exerted in modifying the size and form of the cavities. Inspection of the sea coast demonstrates how, at this day, the wasting and undermining agency of water forms caves very similar, in general character, to those containing fossil bones. In some cases (Kirkdale, Rabenstein in Franconia), it appears probable that the existing valley has been deepened since the time when the cave was tenanted by wild animals, because the mouth of the cave opens on a steep breast of rock several yards above the bed of the valley. Let us admit, then, as sufficiently proved, the existence of open caves and fissures in limestone rocks, at the time when elephants, tigers, hyænas, rhinoceroses, &c. lived in Europe; and inquire further how it happened that their bones came to be entombed in the dark chambers of the rocks.
1. Into open fissures they might fall alive, or be drifted by inundations when dead. It seems difficult to account otherwise for the nearly entire skeleton of a rhinoceros found enveloped in mud and pebbles in the Dream Cavern, near Wirksworth, described by Dr. Buckland (Reliq. Diluv.). Some such mode of explanation must be resorted to for explanation of the accumulation of bones in Banwell Cave, Hutton Hole, and other singular fissures in the Mendip hills. The osseous breccia, as it is called (a mixture of red loam, pieces of stone, and bones), which fills fissures of the calcareous rocks on the Mediterranean coast of Aragon, France (Antibes), Italy (Nice, Pisa), Corsica, Sardinia, &c., appears to have been introduced by currents of water; and from the occurrence of land shells and marine shells and zoophyta in some of these repositories (Villefranche), it is clear that both freshwater inundations, and overflowing of the sea, have influenced the results. The probability seems to be, that the land has there experienced changes of level: in some cases (Palermo) the bones are thought to have been deposited in the sea near ​the shore, and subsequently the whole coast raised. (Pratt and Christie, in Geol. Proceedings.)
2. Into other caves it may be thought other tribes of animals, especially predacious races, might retire to die in quiet. This is the supposition of De Luc, Cuvier, and Buckland, with respect to certain German caves filled to admiration by an enormous mass of bones and decomposed animal matter of extinct species of bears; and the habits of that tribe of quadrupeds, and the circumstances of the caverns, seem to justify this hypothesis, which is also adopted by Blumenbach. In particular, it appears that Rosenmuller has found "bones of a bear so small that it must have died immediately after its birth, and other bones of individuals that must have died in early life." Caves thus characterised are situated in the transition limestone of the Harz and Baüman's Höhle; in magnesian limestone near the Harz (Scharzfeld); in the Carpathians; abundantly in the Jurakalk of Franconia, near the sources of the Mayne (Gailenreuth, Mockas, Zahnloch, Rewig, Rabenstein, Schneiderloch, Kühloch); on the south-western border of the Thuringerwald (Glüchsbrunn, Leibenstein); Westphalia (Kluterhöhle, Sundwick). M. Cuvier states, that the bones in these caverns belong to the same species of animals, over an extent of 200 leagues: that three fourths of the whole belong to two species of bear, both extinct (ursus spelæus, U. arctoideus); two thirds of the remainder to extinct hyænas; a few to a large felis, a glutton, wolf, fox, and polecat.
In all the caverns, M. Rosenmuller found the bones disposed nearly after the same manner; sometimes scattered separately, sometimes accumulated in beds and heaps of many feet in thickness; they occur from the entrance to the deepest recesses; never in entire skeletons, but single bones mixed confusedly from all parts of the animals, and animals of all ages. The crania are generally in the lowest parts of the ossiferous mass, the longer and lighter bones above, the lower jaws always detached from the skull. They are often buried in a ​brown argillaceous or marly earth in which a considerable proportion of animal earth has been detected. No teeth marks are mentioned on the bones, which appear to have been somehow agitated together by the water which introduced the argillaceous loam. This loam sometimes contains pebbles. The general fact is, that on the solid and sometimes worn and polished rock lies a quantity of sand or loam, sometimes 20 or 30 feet thick, full of bones, and over the whole one layer of stalagmite, which has been formed by the droppings from the roof and tricklings from the sides. (Reliq. Diluv.)
KIRKDALE CAVE.
A. Mud on the floor of the cave, one foot thick, including bones.
B. The cavern, usually less than four feet high.
C. Stalagmitic crust over the mud, partly in closing bones.
D. Stalagmitic boss on the crust, derived from dropping water.
E. Stalactites hanging from the roof.
3. It is sufficiently ascertained, that some particular caverns, rich in bones, as Kirkdale Cave in Yorkshire, Kent's Hole at Torquay, &c., have not been filled by inrushing of water, nor by the voluntary retirement of wild animals for shelter or for quiet death, but heaped with bones by ravenous beasts, who used the cavern as a den, and dragged into it the carcases of other more peaceful quadrupeds then living in the vicinity. This inference is so important for the right understanding of the ancient condition of the country, both as to level, climate, and productions, that it appears proper to explain clearly the evidence on which Dr. Buckland founded his opinions.
Kirkdale Cave, accidentally discovered by workmen employed on the road, is about twenty-five miles N.N..E. of York, above the northern edge of the broad vale of Pickering, on the east side of the Hodge Beck, and thirty feet above its waters. (This is from our own measurement.) Its floor is upon the great scale, level for the whole length yet explored,—250 feet,—and nearly conformable to the plane of stratification of the coralline oolite in which it is situated. In some parts, the cave is three or four feet high, and roofed, as well as floored, by the level beds of this rock; in other parts, its height is augmented by open fissures, which communicate through the roof, and allow a man to stand erect. The breadth varies from four or five feet to a mere passage; at the outlet, or mouth, against the valley, was a wide expansion, or antechamber, in which a large proportion of the greater bones, ox, rhinoceros, &c. were found. This mouth was, it is believed, choked with stones, bones, and earth, so that the cave was found by opening upon its side in a stone quarry. On entering the cave, the roof and sides were found incrusted with stalactites; and a general sheet of stalagmite, rising irregularly into bosses and ridges, lay beneath the feet. This being broken through, yellowish mud was found about a foot in thickness, fine and loamy toward the opening, coarser and more sandy in the interior. In this loam chiefly, ​at all depths, from the surface down to the rock (said to have been partially covered by a thin layer of stalagmite under the mud), in the midst of the stalagmitic upper crust, and, as Dr. Buckland expresses it, sticking through it like the legs of pigeons through a pie crust, lay multitudes of bones, of the following animals:—
The hyænas' bones and teeth were very numerous; probably 200 or 300 individuals had left their bodies in this cave: remains of the ox were very abundant: the elephants' teeth were mostly of very young animals: teeth of hippopotamus and rhinoceros were scarce; those of water-rats very abundant.
The bones were almost all broken by simple fracture, but in such a manner as to indicate the action of hyænas teeth, and to resemble the appearance of recent bones broken and gnawed by the living Cape hyaena; they were distributed "as in a dog-kennel," having clearly been much disturbed, so that elephants, oxen, deer, water-rats, &c., were indiscriminately mixed; and large bones were found in the narrowest parts of the cavern. The peculiar excrement (album græcum) of hyænas was not rare—the teeth of hyænas were found in the jaws of every age, from the milk tooth of the young animal to the old grinders worn to the stump: some of the bones are polished in a peculiar manner, as if by the trampling of animals.
This evidence of the former occupation of Kirkdale Cave as a den of hyænas acquires much force by comparing the fragmentary state of the bones of oxen, hares, &c., in it, with the far more complete condition of the same animals in other caves, which, like Banwell, contained few or no relics of hyaena, and with the productions of Kent's Hole, which are similar in all respects ​to those of Kirkdale, and among which hyænas' bones and teeth abound. We may therefore admit, as a thing sufficiently proved on the evidence of caves and ossiferous gravel beds, that Kirkdale, and some parts of the neighbouring country, were dry land in the "elephantine period" of the northern zones of the world. But was the whole of this part of Yorkshire dry land? or was the vale of Pickering a lake, as Dr. Buckland conjectures, on whose margins lived elephants, hippopotami, &c.? an arm of the sea, as the occurrence of a raised shelly beach at Speeton may perhaps lead some to suppose? or a strait connecting the German Ocean with the water which may be imagined to have flowed down the vale of York from the Tees to the Humber, according to the views of some authors on the distribution of diluvium?
Whatever may have been the condition of these comparatively low lands, there can be no doubt that, above the level of Kirkdale Cave (itself only 200 feet above the level of the sea), the land in the N.E. of Yorkshire was wholly dry at the period of the existence of elephants; and this is a point of great importance among the many partial truths which must be established before we can look for a general theory of diluvial deposits.
General Considerations on Diluvial Phenomena.
It will appear from what has been said, that we look upon the erratic blocks, ossiferous gravel and clays, bone caves, and fissures, as phenomena related to a certain geological period, and a particular set of dynamical agencies. Taken as a whole, such a combination of effects is not, at this day, in progress; nor, in general, can we conceive the possibility of their being combined by the concurrence of existing agencies operating with their present intensities, or in their present directions. But considered analytically, there is, perhaps, no single phenomenon of the "northern drift" and the associated gravelly and ossiferous deposits which does not meet a ​sufficient explanation in the known daily operation of physical laws, aided by displacements of the relative level of land and sea, such as geology has established. Compared with tertiary phenomena, we must allow that the pebbly conglomerates on the flanks of the Alps are really detrital deposits of an earlier era. Dr. Forchhammer has adopted the view of the 'boulder formation' of Denmark being one very long series of detrital deposits, including the whole tertiary series, and extending from the plastic clay group beyond the ordinary diluvial epoch.
Whether this be correct or not, it is certain that we must apply, for solutions of the problem of the distribution of the diluvial blocks, to the same agencies which have been invoked to explain the accumulation of the tertiary molasse of Switzerland, and the conglomerates of the red sandstones of England. All their causes we do not know; but the predominant one is known to be great change of the level of land and sea, and the consequent origin of new and powerful oceanic currents.
It is certain that during the 'diluvial' period a large portion of the northern zone, which is now dry land, was under the sea. Murchison has shown that this was not the case in Siberia, which, like other then dry lands, may be regarded as the 'feeding ground' of the mammalia, whose remains characterize some of the deposits we are now considering.
Those ancient sea beds, now dried, show, besides sands and gravels, the effect of strong and variable currents, great masses of fine clay, strangely enclosing far travelled rock masses of various magnitude, much, little, or not at all worn, and occasionally marine shells, in which, upon the whole, an arctic character is recognised.
However this may be, it appears absolutely certain that none but oceanic currents are adequate to explain the extensive ravages of the solid land which produced, ​and the violent currents which distributed, the diluvium. Nor would the ordinary currents of the sea be adequate to the effect. It is requisite further to conceive that the sea was most violently disturbed, either over the points whence the detritus was brought (which supposes those points also to have been under the waves), or at some other situation. In the latter case, we may, perhaps, imagine so great a violence of water to be generated, as to permit the waves to be thrown to some height over the land; and it seems not impossible hereafter, when the geographical relations of the diluvium are well understood, to offer some reasonable explanation of the whole matter, on the principle now known to be true, of great and sudden changes of relative level of land and sea, which, though limited in the area of the masses moved, might have very extended effects through the agency of water. Floating glaciers may also be called to aid the speculation; but they would be useless for any other purpose than to explain particular cases of erratic blocks, and small tracts of peculiarly associated gravel masses.
The best general view of these phenomena recognises in the greater portion of the materials of these deposits the spoils of neighbouring or not far distant land, derived from the sudden ruin of sea cliffs and the gradual waste occasioned by atmospheric action and river erosion. These materials are sorted into gravel beds, sand beds, and broad masses of clay. In addition, we have considerable quantities of far travelled rock masses, often quite unworn, which are so mixed with the fine clay as to indicate the probability that they were not drifted with it by excessive violence of water, but thrown into it, and inextricably mixed with it by a distant operation, the melting or overturning of stone-covered icebergs. Similar stones, but worn and rounded, occur in the gravels, and no doubt have often been washed out of their original sites in the boulder clay. Perhaps it ​was in the latest period of the ice rafts that the large erratic blocks were scattered in greatest abundance.
None of these phenomena appear to require more violent watery movements than such as the sinking and rising of the land must have occasioned, even if it were accomplished by many small gradations. In particular cases, to which the agency of icebergs is inapplicable, excessive local violence of water has been appealed to. For explanation of the bands of angular chalk flints parallel to the axis of the Wealden, Murchison requires the violent concussion of limited tracts, from which he supposes these flint bands to have been mainly derived. There is no antecedent improbability in a postulate of this kind; its necessity must be judged of as a special problem on appropriate evidence.
Zoological and Botanical Character of the Diluvial Period.
The diluvial deposits appear, in general, characterised by the presence of a great number of land animals, and some sorts of trees, which are much more similar to existing forms of life than are the tertiary quadrupeds and plants. But this general or average result requires to be limited by several considerations: first, there are deposits reputed tertiary, as the sandy deposits of Eppelsheim, on the Rhine, in which occur a vast number of species very nearly approaching to existing races; secondly, among the animals of the diluvial period are species, and even genera, as totally distinct from the actual creation as any of the tertiary groups; thirdly, in deposits of undoubtedly tertiary date, as the subapennines of Italy, the sands and marls of the Danube, and flanks of the Carpathians, the crag of Norfolk, bones and teeth of elephant, rhinoceros, mastodon, and other genera of the diluvial period, have been found, though not frequently. It appears, therefore, certain, on this evidence, that the transition from the tertiary to later periods was not accompanied by a sudden ​destruction of old or a general creation of new quadrupedal forms of life. The same appears to be true with reference to the buried forests so often associated with diluvial deposits. It is confirmed by the gradual change in the proportion of existing among extinct species of tertiary shells; so that the most recent groups of tertiary strata contain 40 to 90 per cent, of living forms, while among a dozen or twenty shells in the gravel of Holderness one extinct species is met with.
On the other hand, it must be remembered, that no palæotheria, lophiodontes, or other genera, chiefly belonging to the older tertiary genera, are mentioned as occurring among the diluvial accumulations, though in certain freshwater deposits, as at Gmünd, lophiodontes, oxen, hippopotami, &c. occur together.
Again, certain animals which lived in the diluvial period, as cervus megaceros, appear, by various evidence, not to have been extinct till later times; though we should not venture to adopt Dr. Hibbert's opinion, that they have really lived within the historic ages of Europe. However, it deserves remark, in connection with this subject, that no one has yet succeeded in showing a real and certain distinction between the common red deer and domestic ox of Europe, and the analogous bones of Kirkdale and other caverns.
Upon the whole it seems probable that the palæotherian and other tertiary races of quadrupeds died and became extinct gradually, but not by any one law of uniform progression; that the elephant, and his accompanying tribes, began to exist during tertiary eras, rose to predominance before the close of the diluvial period, and, for the most part, perished in that period, or soon after. Some modern species (stag, ox) were co-existent with the elephant and hippopotamus in northern zones; others (elephas primigenius, rhinoceros tichorhinus), which abounded in diluvial, were also living in tertiary periods; and, perhaps, a few (as the horse) may have been in existence during all these periods. This is a point, however, extremely hard to determine; since, if, ​among living tribes, the diagnosis of species is far from clear, what errors may not be incurred by pronouncing a verdict on the imperfect evidence of a few fragments of detached fossil bones?
Ancient Marine Deposits.
Raised Beaches.—These curious phenomena, first brought prominently forward by M. Brongniart, are a part of the great system of "Pleistocene" deposits, which includes the erratics and drifts. They demonstrate, that within a comparatively modern period, certainly since the actual seas were filled with yet existing mollusca, the beds of these seas have been subject to elevation and depression, so that, in particular places, large quantities of shells attached to their parent rocks, or mixed with the pebbles and sand of their native beaches, have been raised 10, 20, 100, or several hundred feet above high water mark. Within the reach of history, slight displacements of the relative level of land and sea have taken place, as the temple of Serapis near Puzzuoli, Lisbon, Port Royal, are supposed to prove. But these phenomena, connected with local earthquakes and volcanic eruption, are small and limited in comparison with the class of facts noticed above; which appeared to M. Brongniart of so general a character as to justify a supposition that the ocean waters had everywhere suffered a depression of level, even since the creation of existing races of mollusca, and the establishment of the main features of physical geography, though anterior to historic times. To this view of M. Brongniart it is, apparently, a fatal objection, that the levels at which the raised beaches appear, above the sea are extremely varied, even on points of the coast of the same country, and much more when we compare distant coasts; whereas, upon his view of a general lowering of the surface of the sea by one depression of the crust of the globe (affaissement de la ​croûte du globe dans un point), we should see accordant indications of the former height of the water.
The following examples are selected to illustrate the nature of these deposits:—
On the coasts of Great Britain, phenomena of this kind have been observed in the valleys of the Forth (Boue, Maclaren) and the Clyde (Laskey), chiefly in the form of low terraces considerably above the actual flow of the tide; on the coast of Lancashire, about Preston (Gilberston); at the base of the Forest Hills, and other places in Cheshire (sir P. Egerton); near Shrewsbury; on the Mersey at Runcorn; and on Moel Tryvaen, near Caernarvon (Trimmer).
That an uplifting of the shores of the Moray Frith has taken place subsequent to its having assumed its present outline, is considered by Mr. Prestwich as proved, by the existence, in several places, of a raised beach. In Banffshire, this beach varies from six to twelve feet above the present high water level; and contains shells now inhabiting the neighbouring sea, as patelia vulgata, patelia lævis, trochus ziziphinus, littorina littorea, turbo retusus. At Gamrie, celebrated for its ichthyolites, Mr. Prestwich found, in light-coloured sands, associated with rolled gravel and dark clay beds, the following recent shells:—Astarte Scotica, tellina tenuis, buccinum undatum, natica glaucina, fusus turricola, dentalium dentalis, &c. They were extremely friable, but perfect. The deposit attains, in some places, a thickness of 250 feet, and rises to a height of 350 feet.
On Moel Tryvaen (1450 feet above the sea), the shells (buccinum, natica, turbo, Venus) were in fragments, adhering to the tongue, very much as in some tertiary deposits: they lie in sands and gravel, with granite boulders, 1000 feet above the sea, the country between them and the Menai being greatly broken, the rocks below the bed of shells worn and scratched by the drifting of the pebbly masses.
In Cheshire, the shelly gravel and sands, containing ​turritella terebra, murex erinaceus, and cardium edule, are covered by the ordinary sandy diluvium of Cheshire, in which are many erratic blocks from the North of England, as well as pebbles from the Welsh border.
In and near the valley of the Ribble, for some miles inland, from its mouth, near Blackpool, by Preston to the base of Longridge fell, and on Whittle hills, from the level of the sea to 300 feet above it, occur beds of marl, sand, and gravel, under the ordinary diluvium with erratic blocks, locally full of shells of mollusca now living on the neighbouring coast—such as turritella terebra, cardium edule, tellina solidula, &c. The lamination of these shelly beds is irregular, resembling a modern beach accumulated under the influence of strong currents.
Somewhat different appearances are seen in the opposite parts of Yorkshire, especially in the district of Holderness, where sandy and gravelly beds, full of pebbles and fragments of Cumbrian rocks, contain, at particular spots (Brandsburton, Paul, Ridgmont), layers of shells, all marine, and all, except one, now living in the neighbouring seas. Besides the strong shells of turbo littoreus, purpura lapillus, and buccinum undatum, we have mya arenaria, teilina solidula, t. tenuis, mactra subtruncata, cardium edule, &c.; and it is certainly very strange to discover these and other tender shells in a good state of conservation among the twisted and confused laminæ of so coarse and irregular a deposit as that in the vicinity of Ridgmont.
On the same coast, at Speeton, is a much more regular sandy deposit full of cardium edule, amphidesma Listeri, tellina solidula, &c., on the top of the cliff.
From the Wexford coast of Ireland, Mr. Griffith produced at the Dublin meeting of the British Association, shells of existing, and also of extinct, species, from what seemed a raised beach. A similar deposit, on a very extensive scale, occurs on the coasts of North and South Devon and Cornwall. (Murchison, Sedgwick, De la Beche, &c.) ​
From these short notices, the reader may be assured, that, even on the British coasts, the phenomenon of raised beaches is one of the most general yet known: that the deposits called by this name were accumulated under considerably different circumstances, is certain; their high antiquity is proved by the superposition (in general) of the erratic boulders; and the general analogies they offer to the Sicilian and other tertiary deposits are obvious and important. A philosophical study of these till lately neglected phenomena will certainly reward investigation, and probably strengthen in a high degree the basis of geological induction.
Turning to other countries, we find abundance of analogous facts. As on the south coast of England, so on the north coast of France, on the hills of St. Michel, formations of the nature above described occur, and have been described by M. Fleuriau de Bellevue and M. Brongniart, under the name of "gravier coquillier." The shells of St. Michel consist of many species, univalves and bivalves; the two pieces of the latter often remaining in their proper position; the whole retaining both their natural colour and texture, and lying as similar shells are associated at this day on the neighbouring coast Ostrea edulis, anomia ephippium, pecten sanguineus, modiola barbata, murex imbricatus, buccinum reticulatum, are mentioned as the principal species. They are placed nearly fifty feet above the sea. At Nice, similar banks occur at nearly the same elevation; the coasts of Sicily, Greece, and Asia Minor, give similar evidence.
Both on the Baltic and the Atlantic coasts of the Scandinavian peninsula, phenomena of the same nature have been long known and rendered famous by the relation they bear to the hypothesis of the gradual subsidence of the level of the Baltic. Von Buch, Brongniart, Strom, Lyell, and Forchhammer have investigated the facts with attention and success. On the western coast of Sweden, at Uddevalla in the province of Gotheburg, in a little bay of gneiss rocks, occurs so vast a quantity of shells, ​70 metres (76 yards) above the sea, that they have from time immemorial been collected for use on foot-paths. In hollows of the gneiss rocks, M. Brongniart found balani yet adhering, and detached fragments to prove the interesting fact.
In a recent visit to Sweden, Mr. Lyell has confirmed and extended these observations, and connected the results with the general question of subterranean movements and the local speculation of the lowering of the Baltic,—an expression which may very properly be transformed into a rising of the borders of that sea. Near Stockholm, remarkable ridges of sand and gravel, called sand oasar (asar), 50 to 100 feet high, range north and south, and yield good road materials. Under one of these ridges in the same sand and gravel, 30 feet above the Baltic, are found shells in abundance, such as now live in the Baltic, viz., cardium edule, tellina Baltica, mytilus edulis, littorina crassior, l. littorea, &c. At other spots, 70, 90, 100 feet above the sea, shells in general similar to the above (with neritina fluviatilis and bulimus lubricus, a land shell) were found abundantly, about Stockholm, Upsala, and Gefle; and sometimes covered by erratic blocks (Upsala). It was noticed at Uddevalla, that several species of fusus occur there, though none are now found in the Baltic. From the whole investigation it appears certain, that both on the Atlantic and the Baltic shore, the land has in some ancient periods risen considerably (200 feet at least), so that Lake Wener on the west, and Lake Maeler on the east, were formerly parts of the ocean: it also appears probable, that a part of the Scandinavian peninsula is, at this day, gradually rising higher above the sea, but this rise does not affect the south of Scania; the rate of rise is supposed to be three feet in a century at Lofgrundet, north of Upsala.
In connection with this subject, we may mention the extended deposits of sea shells (though their identity with existing species may be doubtful) on the plains round the Caspian; the shelly sands at the Cape of ​Good Hope; the elevated terraces of shells on the coast of Valparaiso, and on the plains of Patagonia; the coral masses in the interior of Antigua; the shelly beds of Barbuda; the Keys or sand islands on the coast of Florida; and the sandy portion of the Atlantic plain which borders the United States (Rogers, in Brit. Assoc. Reports); for it seems difficult not to recognise, in these and many other examples, proof of the very great extent to which the level of land and sea has been and still is locally variable.
From what has been already stated, it may be inferred that, since the completion of much of the tertiary system of strata, the northern zones of Europe and America have been deeply submerged below an ocean which in several parts at once, perhaps in all parts at different times, was traversed by arctic currents, if it had not perpetually a boreal character. This ocean has been repelled by the uprising of the land, and the ancient deposits remain, in part, on the now dry ground. Only in part, for by the agitation of the sea at the uprising, and the subsequent action of atmospheric forces, much of the old sea bed has been worn away and removed. The raised beaches are some of the littoral parts of this bed. They are not now necessarily at one constant height above the sea, for the upward movement may not have been to the same vertical amount at different points; nor have they necessarily one mineral or structural character; nor must they necessarily contain all the same shells or other organic reliquiæ. In this latter particular they may vary, not only because of any original local diversity of the fauna, at one epoch, but also because the beaches may have been raised at different times, or from other causes may contain the remains of different periods.
Under these circumstances it may appear hopeless to determine, amongst the raised beaches, more than very vague relations to geological time. We know that they belong to a very late class of tertiary formations, and that their antiquity is such as to put them far beyond the scope of modern deposits. ​
While some, perhaps, reveal to us the inhabitants of the sea before the period of glacial deposits, many certainly contain the reliquiæ of that period, and a few may be admitted as of a later date.
Professor E. Forbes has lately collected into a general view the somewhat scattered information on this subject, which since the date when Linnæus explored Uddevalla (1747), has found no more zealous inquirer than Mr. J. Smith. An extremely valuable contribution to the zoology of the glacial sea was brought by the Geological Survey of Ireland under the direction of Capt. James, In the following table the numbers of testaceous mollusks of four well ascertained modern faunas are compared with a summary of the testacea belonging to the glacial formations of the British Isles.
| Orders of Mollusca. | Comparative Table of Testacea Inhabiting | Comparative Table of Testacea Inhabiting | Comparative Table of Testacea Inhabiting | Comparative Table of Testacea Inhabiting | Comparative Table of Testacea Inhabiting |
| Orders of Mollusca. | Mediterranean. | British Seas. | Seas of Massachusetts. | Seas of Greenland. | Fossil in British glacial Beds. |
| Cephalopoda with shells | 1 | 1 | 1 | | |
| Pteropoda | 13 | 1 | | 2 | |
| Nucleobranchiata | 6 | 1 | | | |
| Gasteropoda | 368 | 248 | 100 | 74 | 63 |
| Lamellibranchiata | 200 | 210 | 83 | 44 | 63 |
| Palliobranchiata | 10 | 4 | 2 | 1 | 1 |
| Totals | 598 | 465 | 186 | 121 | 124 |
"This glacial marine fauna is composed of living British species of northern origin, some of which are now confined to climates far colder than our own, with a few forms supposed to be extinct, and one or two shells of southern origin, or known only in the crag." Its analogy to the modern fauna of Greenland and the northern coasts of America is evident. ​
If the bed of the sea were now raised round the British Isles, so as to expose its deeper parts, we should have some differences in the shells laid bare according to the original depths at which they lived. We should distinguish, by the aid of Forbes' s dredging, the old littoral or tidal zone everywhere by patella vulgaris; if rocky, by littorinæ; if sandy, by cardia, tellinæ, solenæ; if gravelly, by mytili; if a clay bottom, by lutrariæ and pullastæ. The laminarian or subtidal zone, extending to 15 fathoms, would give us lacunæ and rissoæ, patella pellucid and p. lævis, trochus ziziphinus, and various modiolæ. The coralline zone, extending to 50 fathoms, would show a great variety of carnivorous mollusca; fusus antiquus, pullastra virginea, pecten maximus, and pleurotoma teres being characteristic. And in the deepest of the zones, that of deep sea corals, which goes beyond 100 fathoms, we should have a more contracted series of mollusca, but including brachiopoda and ditrupa.
What in fact we have in our raised beaches, and shelly gravels and clays, is a series of littoral, subtidal, and shallow sea shells, without the deep sea corals. They do not, however, lie as shells might be found in undisturbed parts of the old sea bed; on the contrary, they are frequently rolled, and much broken, as if drifted by water, and crushed by pressure.
We may compare with these results what has been learned in late years concerning the circumstances under which mineral matter is aggregated and the conservable parts of living beings preserved under the sea. ​
Marine Deposits in Progress.
The elevated portions of the borders of the modern oceans which have been noticed, are so fraught with instructive analogies to the processes of nature in more ancient times, that we cannot help feeling regret at the limited means which man possesses of penetrating the great deep, and watching the phenomena which happen on its quiet bed. There we should behold, it is probable, a number of circumstances connected with the life of marine mollusca, radiaria, Crustacea, fishes, which would throw quite a new light on many of the problems of old geology; inform us of the probable depths, distance from the shore, and river mouths, and other conditions most important for us to know in constructing trustworthy inferences regarding the formation of the fossiliferous rocks.
Coral Reefs.—That the very deep parts of the sea (nine miles is a probable estimate for the Atlantic depths) are as devoid of life as the centre of an African desert of moving sand, is extremely probable, from the known fact of the dependence of organic life on air and light; the former must be greatly modified, the latter extinguished, in passing through such a mass of absorbent fluid. The voyagers of modern date (captain Beechey, MM. Quoy and Gaimard, Freycinet, Stutchbury, Darwin) concur in removing one error of importance on this subject; they have rendered it highly probable that the coral reefs and coral islands which abound so much in the Pacific Ocean, do not rise from even the depth of many hundred yards, but commence on the summit of some volcanic elevations, or other submarine ridges and rocks, not far below the surface of the sea.
These coral islands and reefs, which may be viewed as lines of islands, are certainly remarkable for their extent and mass of matter, even as compared with the ancient calcareous rocks, which derive much of their ​substance from zoophytic exuviæ. They form the basis of, or surround, the shores of most of the islands in the warm parts of the Pacific, and stretch for a thousand miles parallel to the north-east coast of Australia, in a narrow reef of several hundred miles' length. In like manner, about the Indian and West Indian islands, in the Red Sea, Persian Gulf, and Mediterranean, coral abounds, so as to constitute a considerable portion of the products of the sea.
It has long been the custom to compare the rapid and abundant growth of coral islands with the limited breadths of marine limestone which lie amidst the sedimentary sandstones and shales of the stratified rocks; and on the comparison conjectures have been founded that the stony crag of Orford, the coral rag of Wilts, the transition limestone of the Eifel and Plymouth, were, in effect, ancient coral reefs. It appears, on a first glance, a fatal objection to this view, that these ancient rocks are regularly stratified; the corals in them occupying particular (often thin) beds, not lying confusedly through the mass, nor growing one to another, so as to resemble in structure what is popularly understood by a coral reef. But this notion of a coral reef, exact enough in many instances, is incorrect when applied to the Bermudas, which grow up a mingled mass of coral, shells, comminuted calcareous substances, and sands drifted by the current of the gulf stream. Parts of this calcareous mass, raised above the sea in hills, are drifted by the wind and dispersed into beds. In such accumulations, not far from land, under the influence of sea currents, we ought to find very different results from those which take place in the broad calm waters of the wider ocean.
In Mr. Stutchbury's excellent dissertation on the formation and growth of coral reefs and islands (West of England Journal), the construction of the principal part of the coral mass is ascribed to the genera caryophillia, meandrina, astræa, porites, and madrepora; while the ​ornamental parts are made up by a diffusion of the other forms of Linnæan madrepores, viz. fungia, pavonia, agaricia, monticularia, echinophora, pocillopora, seriatopora, and oculina, together with gorgonia, isis, corallium, melitea, coralline, spongia, alcyonium, actinia, &c., independent of the locomotive asteriæ, echini, testacea.
The coral islands are classed by Mr. Stutchbury as circular, flat, long narrow, and encircling high land.
The coral islands of the Dangerous Archipelago (lat. S. 12° to 27°, long. W. 130° to 155°) are all of the first kind, and consist of strips or belts of coral of an annulate or circular form, from 400 or 500 yards to one mile across the ring which always incloses a lagoon; seldom raised above the water more than from 4 or 5 feet; abrupt towards the ocean, which rapidly deepens to more than 120 fathoms. The islands vary from 2 or 5 to 150 miles round; the ring, being often divided across by a fissure, admits vessels to enter the lagoon. The depth at which the coralligenous zoophyta commence their labours is said not to exceed 15 or 20 fathoms (Quoy and Gaimard say 20 or 30 feet, Mr. Darwin has recently given the same estimate as Mr. Stutchbury). The bottom of the lagoons is seen in calm weather at a depth of 100 feet or more, strewed over with dead shells and broken fragments of coral, rarely showing any living specimen below sixteen or seventeen fathoms; at which depth, smaller reefs rise within the lagoon; and beyond which depth, broken masses of rock may be seen without any living portion attached.
It would appear that, during the formation of a reef, portions of it become compact, and as dense as any limestone rock; a circumstance indicative of the partial dissolution and re-precipitation of the coral masses, and apparently analogous to the process whereby coral shells, &c. have been imbedded in the compact limestone of ancient stratified rocks. Extensive beds of particular shells appear among the islands.
Islands often occur of a fiat or tabular form, generally ​oval or irregularly rounded at their circumference: of this form are the group called by Cook the Friendly Isles, consisting of numerous islands, the majority of which are tabular.
There are also many crescent-shaped reefs, with the most convex portion of their arc the highest, often denoting themselves to the mariner only by the breaking of the waves, and here and there a rock above the level of the ocean, while the horns of the crescent are depressed, and gradually lost in the greater depth: in a few instances, as at Gambier's Island, they are sufficiently raised to have become verdant and inhabited.
Of those which form long narrow strips of land, Mr. Stutchbury refers to Tehuro, a few leagues from Tahiti, and the great reef which takes the course of the north-eastern shore of New Holland, which Captain Flinders describes as being more than 1000 miles in length: in the course of which there is a continued portion exceeding 350 miles with scarcely a break or passage through it.
Of the last group of coral islands, or rather reefs, encircling elevated land, the Society Islands, including Tahiti, offer striking examples; being often surrounded by coral reefs, generally situated 400 or 500 yards off shore, with a deep channel between, having numerous openings, through which ships can enter and lie at anchor in perfect safety. These breaks in the coral barrier are, in most instances, opposite the mouths of freshwater rivulets.
The islands Raiatea and Tahaa (Ulietea and Otaha of Cook) are divided by a strait, by which ships can enter at the windward side of the islands, and get to sea again through the leeward channels. These two islands are entirely surrounded by one coral reef, extending throughout the circumference of both; the openings through the reefs are, in most cases, denoted by the points being rather higher and more verdant, having trees, principally cocoa nut trees, planted by the natives upon them. The passage is seldom more than 100 ​yards in breadth, with the depth varying from 3 to 15 fathoms.
The dark part is calm water round the islands and within the coral reef. The arrows show the entrances and exits for vessels.
The form of the coral islands must very materially depend upon that of the base on which they happen to be built; hence their circular, lunulate, oval, or irregular forms give information as to the shape and even nature of the subjacent rocks. In most cases, the base of the small islands appears to be a volcanic crater, entire or broken; islands of volcanic rock, as Tahiti, are surrounded by rings of coral. The elevation of the coral islands is not owing to the mere accumulation by the rough action of the sea, but to a gradual rising of the low islands, and a violent subterranean movement of the lofty ones, like Tahiti, which bears on the apex of one of the highest mountains a distinct and regular stratum of semi-fossil coral, and near it, but on a lower level, a volcanic crater with two lateral gorges.
In this case, had the upward movement been gradual, why should not the coral growths have covered the edges of the crater, or rested on other points?
Mr. Darwin has recently been conducted, by a consideration of the structure of coral islands, annular and
distance guarding, insulated points or long coasts of land, to a remarkable general speculation; viz. that in the Southern Ocean the distribution of the coral masses on a great scale, and their peculiar forms in detail, are explicable on the supposition of certain lines, or rather, long narrow spaces of ocean, in which the land has undergone and is still suffering gradual depressions, and alternating with these other long spaces in which the land is rising. Where depression has taken place, coral is supposed to have grown on the submerged points; and, as the depression proceeded, to have continued to grow and keep the surface as high as the sea. A depressed mountain chain might thus be the origin of a long line of coral islands, or of a continuous reef, as on the east coast of New Holland; a single island of rock, at first skirted by a fringing growth of coral, would, upon further depression assume the appearance of a central rock, and a circular ring of coral; and, finally, the rock would vanish, and nothing but an annular coral reef appear, in closing a lagoon, which might subsequently be filled up. The principle of this explanation may be understood by reference to the figures annexed, where $a^{1},a^{2},a^{3},a^{4}$, are successive levels of water, surrounding and finally covering the insulated rock r, upon which, at c, coral began to grow where the depth was small enough. On a further subsidence, more coral, $c^{2}$, was added upon, but not within, the reef e; and, finally, $c^{3}$ being raised to the surface of the sea, while
off by waves filling up the space between the reef and the rock, the whole became an annular coral reef in closing a lagoon. The island and reef would thus present in a plan the following features successively.
In fig. 1. the rock is skirted by coral; in fig. 2. the rock is separated from the coral which widely encircles it by a channel of (deep) water; in fig. 3. the rock is not seen, but forms the base of the lagoon, and is covered by fragmented corals.
If, instead of a sinking, we next imagine a gradual rising or a stationary situation of some island, on which a circle of coral was fixed, the additional growth of this substance would be always on the outside, and the land would never be separated from a widely encircling reef by a channel of deep water.
In Mr. Darwin's views, the presence of a lagoon coral island is an evidence of depression of the solid land there; and, on the contrary, marginal coral reefs often supply evidence of rising, in addition to that furnished by shelly beaches at high levels. Thus may ​we comprehend, in the former case, the formation of a long bank of coral, by the successive submersion of a line of mountain summits; and the filling of a sea with many small annular reefs, by the sinking of island rocks: in some cases, the circular form of lagoon islands may, however, be as well understood by supposing them to have grown on a submarine volcanic crater. A decisive proof of the truth of Mr. Darwin's views, in the particular instance, would be the discovery of solid coral rock at a much greater depth than that which is stated to limit the existence of the lamelliferous polypi.
The general results of and views arising from Mr. Darwin's investigations include the following very important points:—
1 . That linear spaces of great extent in the equatorial regions are undergoing movements of an astonishing uniformity, and that the bands of elevation and subsidence alternate.
2. From an extended examination, the points of volcanic eruption all fall on the areas of elevation. The importance of this law is evident, as affording some means of speculating, wherever volcanic rocks occur, on the changes of level even during ancient geological periods.
3. Certain coral formations acting as monuments over subsided land, the geographical distribution of organic beings is elucidated by the discovery of former centres, whence the germs could be disseminated.
4. Some degree of light might thus be thrown on the question, whether certain groups of living beings peculiar to small spots are the remnants of a former large population, or a new one springing into existence. (From Geol. Proceedings, 1837; and notes taken during the reading of Mr. Darwin's paper to the Geol. Society.)
Shell Beds.—What the circumstances are, which favour in a special degree the accumulation of shells on the bed of the sea, may be partly conjectured; but ​the subject deserves to be considered as one of the most important problems which geology looks to the naturalist to resolve. Very different conditions are known to govern the aggregation of the different tribes: they choose different soils—so to speak love—different depths, bear unequally the influence of currents, fresh water, climate. Oysters, for example, by their stationary habits and mutual attachment, exclude nearly all other conchifera from those patches of the sea where they thrive. So, among the fossil ostreæ we find whole beds of vast extent; in the Kimmeridge clay (O. deltoidea), and in the lias (gryphea incurva). Near the muddy mouths of tide rivers, uniones, anodontes, &c. abound, and are little mixed with other genera; and their ancient prototypes in the estuary deposits of the coal tracts and Wealden formation are similarly circumstanced. Donati found the Adriatic covered with shells and sediments almost identical with the subapennine deposits; the German Ocean yields sands and shells like those of the raised beach at Speeton; the Bay of Morecambe, upraised would resemble the deposits at Preston; the Baltic bed, with its living shells, is like the undulated gravel heaps and buried testacea of Sweden; and there can be no doubt that a careful scrutiny of the borders and bed of the existing sea would show many conchiferous formations in progress extremely like those of ancient date. It appears a very general fact, that the existence of living marine testacea is limited to a small depth from the surface. In Mr. Broderip's table (De la Beche's Theoretical Researches), the greatest depth mentioned (for terebratula) is 90 fathoms. It is much to be wished that this interesting subject should attract the attention of the scientific officers of the British navy.
We are indebted to Professor E. Forbes for a large series of valuable results obtained by researches in the Ægean Sea, since the preceding observations were written. In respect of depth the Ægean may be divided into 8 zones, viz:— ​
1. Littoral zone, not exceeding 2 fathoms in depth, its ground various.
2. Zone extending from 2 to 10 fathoms; mud or sand.
3. Zone extending from 10 to 20 fathoms; gravelly or sandy.
4. Zone extending from 20 to 35 fathoms; mud and gravel.
5. Zone extending from 35 to 55 fathoms; nullipore and shells.
6. Zone extending from 55 to 79 fathoms; nullipore.
7. Zone extending from 80 to 105 fathoms; nullipore chiefly.
8. Zone extending from 105 to 230 fathoms; yellow mud.
In this sea occurred 3 Cephalopoda, 8 Pteropoda, 10 Nucleobranchiata, 16 Nudibranchiate Gasteropoda, 60 Inferobranchiate, Tectibranchiate, Scutibranchiate, Cyclobranchiate and Cirrhobranchiate Gasteropoda; 1 Pulmoniferous Gasteropod; 190 Pectinibranchiate Gasteropoda; 8 Brachiopoda, 115 Dimyarian Lamellibranchiata, and 28 Monomyarian Lamellibranchiata, 17 Tunicata; 57 Arachnodermata, 47 Echinodermata; of Zoophytes not many species; of sponges 20.
To all these Professor Forbes assigns the characteristic regions of depth, nature of favourite ground, and geographical distribution. The most positive and determining influence is that of the ground or sea-bottom. "According as rock, sand, mud, weedy or gravelly ground prevails, so will the numbers of the several genera and species vary. The presence of the sponges of commerce often depends on the rising up of peaks of rock in the deep water near the coast. As mud forms the most extensive portion of the bottom of the sea, bivalve mollusca abound more individually, though not specifically, than univalves. As the deepest sea bottom is of fine mud, it is there the delicate shells of pteropoda and nucleobranchiata are preserved. Where the bottom is weedy, we find the naked mollusca more numerous than elsewhere; where rocky, the strong shelled gasteropoda and active cephalopoda. Few species, either of mollusca or radiata, inhabit all bottoms indifferently." ​
The following diagram exhibits the comparative characters and relations of the several regions:—
| Sea Bottom— Deposits forming. | Region. | Extreme Depth in Fathoms. | Characteristic Animals and Plants. |
| 12 Feet—Ground various, usually rocky or sandy, conglomerates forming. | I. | 2. | Littoriua cserulescens. Fasciolaria tarentina. Cardium edule. Plant:—Padina pavonia. |
| Ground muddy, sandy, or rocky. | II. | 10 | Cerithium vulgatum. Lucina lactea. Holothuriae. Plants:—Caulerpa, Zostera. |
| Ground mostly muddy or sandy: mud bluish. | III. | 10 | Aplysiæ. Cardium papillosum. |
| Ground mostly gravelly and weedy, muddy in estuaries. | IV. | 35. | Ascidiae. Nucula emarginata. Cellaria ceramoides. Plants: Dictyomenia volubilis. Codium bursa. |
| Ground full of nullipores, and shelly. | V. | 55 | Cardita aculeata. Nucula striata. Pecten opercularis. Mvriapora truncata. Plant: Rityphlæa tinctoria. |
| Ground mostly nulliporous, rarely gravelly. | VI. | 79 | Venus ovata. Turbo sanguineus. Pleurotoma maravignæ. Cidaris hystrix. Plant:—Nullipora. |
| Ground mostly nulliporous, rarely yellow mud. | VII. | 105. | Brachiopoda. Rissoa reticulata. Pecten similis. Echinus monilis. Plant: Nullipora. |
| Uniform bottom of yellow mud, abounding for the most part in remains of Pteropoda and Foraminifera. | VIII. | 230 | Dentalium 5-angulare. Kellia abyssicola. Ligula profundissima. Pecten Hoskynsi. Ophiura abyssicola. Idmonea. Alecto. (No plants). |
Zero of animal life probably about 300 fathoms.
Serpentine appears actually to prevent the abundance of shelled mollusca. The character of the water, the proximity of river-mouths, the set of currents, are all elements of local distribution; but after allowance is made for all these circumstances, depth in the water remains to be considered.
In the following table the numerical distribution of shells in the various regions of depth of the Ægean is expressed.
Classes of Shells.
| Regions of Depth. | Multi- valves. | Patel- liform. | Tubu- lar. | Holos- tomata. | Siphon- ostomata. | Pteropoda and Nucleo- branchiata. | Brachi- opoda. | Lamelli- branchiata. | Total in each Region. |
| I. | 3 | 11 | 4 | 50 | 40 | 1 | 0 | 38 | 147 |
| II. | 2 | 3 | 4 | 40 | 27 | 0 | 0 | 53 | 129 |
| III. | 0 | 2 | 2 | 40 | 27 | 0 | 0 | 53 | 129 |
| IV. | 2 | 3 | 2 | 44 | 41 | 0 | 2 | 68 | 142 |
| V. | 2 | 5 | 1 | 35 | 36 | 0 | 4 | 58 | 141 |
| VI. | 1 | 6 | 1 | 28 | 30 | 0 | 5 | 48 | 119 |
| VII. | 1 | 6 | 2 | 17 | 16 | 3 | 7 | 34 | 85 |
| VIII. | 0 | 1 | 2 | 15 | 5 | 12 | 3 | 28 | 66 |
| Total species. | 7 | 20 | 6 | 115 | 104 | 12 | 8 | 135 | |
| Total occurrences in depth. | 11 | 37 | 18 | 269 | 225 | 16 | 21 | 379 | |
| Ratio of number of occurrences to number of species. | 1.6 | 1.8 | 3.0 | 2.3 | 2.1 | 1.3 | 2.6 | 2.8 | |
To all the eight regions only two species of mollusca are common, viz. area lactæa, cerithium lima. Nine are found in six regions, seventeen in five regions. The observed distribution of other species which occur in more than one region agrees with a general inference that the extent of range of a species in depth is proportioned to the extent of its geographical distribution. ​
Supposing, what is believed to be true, that the shelly inhabitants of the sea, like the zoophytic tribes, exist in abundance only to a small depth (say 1000 feet), it must follow, that during the formation of the stratified crust of the earth, very general and long continued depression occurred in the ancient bed of the sea: for as the series of strata, full, at least partially, of organic remains, which lived on or near the spots they now occupy, exceeds in almost all countries many thousands of feet in thickness, the successively deposited surfaces of strata must have successively sunk lower and lower, till the whole depressing force being exhausted, a contrary action raised them again. To this highly important subject we shall recur in another part of this treatise.
It is further deserving of remark, that if, at this day, contemporaneous deposits of pebbles, sand, clay, and calcareous matter happen even in the same oceanic bed, as the bottom of the German Ocean, each strewed with different groups of shells, the distribution of organic fossils in the different primary and later strata, if at all governed by the same laws as those now traceable in nature, though affected by some general characteristics of period, must also exhibit specific relations to the nature of the rocks. We have already shown this to be the fact; and it serves to strengthen our confidence in the reasoning employed, when we find the results of the same causes harmonise in the most ancient as well as the most modern instances.
Banks of Sand, Clay, Gravel, &c.—A very slight observation of the action of the marine currents on our shores is enough to determine many circumstances regarding such accumulations. The first remarkable act is the sorting of the mingled materials brought down to the sea by inundations from steep land, like the maritime Alps, or gathered from the falling cliffs by the action of the waves. According to specific gravity and magnitude, the masses are separated, transported, deposited—pebbly deposits lie under the gravelly cliffs— ​the sands are swept to a greater distance—the fine clay carried far in the waters. Of all these circumstances the English coasts offer abundant examples—especially Teesmouth, the Bristol Channel, and the Bay of Morecambe, which, on their wide sands, present a wonderful variety of appearances, proper to furnish the speculative geologist with more accurate and applicable data than are commonly relied on. Among others, the aspect of the surface of the sand—its ripple marks, varying in an exact proportion to the depth of water and the direction of the wind—the numerous little valleys and rills which modify the slopes—the countless prints and seeming prints of the feet of birds—the trails of mollusca and annulosa, may suggest to the reasoning geologist proofs of the important truth, that all our laminated sandstones and flagstones were littoral deposits,—a point of departure for accurate inferences concerning the rising and falling of the level of the land, as compared with that of the sea.
It is hardly necessary to observe, that the nature of these deposits varies with that of the supply; near pebbly cliffs, the shore is a shingly beach; low sandy cliffs, or a rough river, cause expanded breadths of sands sloping gently to the sea; on an argillaceous coast, the bay may be full of sand, drifted by littoral currents, which very much modify all the ordinary results, and are the principal agents in first wasting the high ground, then filling up the low parts of the shore, and thus depositing new land, which subsists either by a natural defence of blown sand, gathered pebbles, or the prudent skill of the engineer, till some unheard-of storm returns to reclaim again the gradual gift of generous nature, or the bold theft of craving man.
The distance to which currents can transport solid matter in the ocean may be well illustrated by the action of the gulf stream which sweeps from the Guinea coast by the Gulf of Mexico, and then traverses so great a portion of the North Atlantic; for it carries timber and tropical fruits within the influence of the ​littoral in draughts of Iceland, Norway, and Ireland; and Col. Sabine's observations on the sea current of the Maranon show, that, at a distance of 300 miles from its mouth, the fresh water of that mighty river floats on the heavier water of the sea, and retains its earthy discoloration.
* ↑ Rogers, in Reports of Brit. Assoc. voL iii. Dr. Bigsby's Observations on the travelled Boulders about Lake Huron and Lake Erie (Geol. Trans. vol. vi. pt 2.).
* ↑ See Lyell's Geology, Brongniart, Tableau des Terrains; De Luc's Letters, &c.
* ↑ Sabine, in British Association Reports, 1843.
* ↑ See Geology of Russia, p. 547, for an excellent illustration of the Author's meaning.
* ↑ Mr. Trimmer refers some singular phenomena in the Cromer cliffs to melting of buried ice (Geol. Proceedings).
* ↑ Proc. of Geol. Soc., 1848.
* ↑ Ibid., 1852.
* ↑ Forbes in Mem. of Geol. Survey, vol. i.
* ↑ Reports of British Association for 1850.
* ↑ Buckland, Reliquiæ Diluvianæ; Murchison, Geol. of Russia; Rogers, to Proc. of American Naturalists.
* ↑ Geol. of Russia, p. 494.
* ↑ Forbes, Mem. of Geol. Surrey, vol. i.
* ↑ Trimmer in Geol. Proceedings, 1851.
* ↑ Geol. Proc., 1852.
* ↑ Geological Proceedings, 1837.
* ↑ Geological Proceedings.
* ↑ Mem. Wern. Soc., 1837.
* ↑ Mem. Geol. Survey, vol. i. p. 367.
* ↑ Ibid. vol. i. p. 369.
* ↑ In De la Beche's "Theoretical Researches," a small and interesting map illustrates this supposition. Mr. Austen has investigated the bed of the English Channel, as known by soundings. The German Ocean is likewise thus familiar to geologists. The extended and persevering research of Prof. E. Forbes has brought a great part of the British marine fauna into systematic tables, according to depth, character of ground, and geographical position. (Rep. of British Association, 1850.)
* ↑ Neilson, Geol. Soc. Proceedings.
* ↑ Reports of British Association, 1843.
FLUVIATILE AND LACUSTRINE DEPOSITS.
WE now quit the marine deposits of tertiary and post tertiary age, and fix our attention on a parallel series of accumulations, in valleys, and ancient lakes, for the most part under the influence of fresh waters. In treating of formations in valleys, we cannot always confine our illustrations to the operations of fresh waters, because continued research appears, in several instances, to show that what appeared at first to be due to lacustrine fluctuation or river currents was really the effect of water-movement in an ancient arm of the sea. This result is quite to be expected. Valleys have been the channels of strong sea currents before they were raised above the ocean and filled with precipitations from the air: valleys were sub aqueous before they became subaerial, and in them we ought to find marks of marine followed by other marks of fluviatile action.
When shells are absent (as they most frequently are), we may not always be able to distinguish between the beaches left by the retiring sea and the banks left by rapid inundations formerly flowing at higher levels. ​
No uncertainty of this kind is felt in tracing the history of the purely lacustrine deposits: for these seldom are deficient in the characteristic organic forms of fresh water. Perhaps in both of these classes of phenomena, we may reasonably look for more zealous and persevering research than have been lately bestowed upon them. Old lakes deserve all the attention of palaeontology and physical geology: for their history goes far back on the scale of geological time, and by their contents we know at least somewhat of our "native" land in Pleistocene, tertiary, oolitic, and perhaps carboniferous periods. Nor is any survey of the primeval world at all complete which fails to inquire into the river action of early geological times, since this action is an index of the state of the land, and many of our valleys are even of palæozoic date, and contain conglomerates heaped in them by palæozoic, mesozoic, and cainozoic waves. And, even where no trace of the valley remains, we not infrequently mark the positive effect, or the probable vicinity, of a great ancient river. Thus, in the Weald of Sussex, we have such a combination of reliquiæ as to mark, not a bay of the sea, but an estuary nourished by a richly wooded river; nor can we easily escape from the conviction that the alternating sediments of the coal formation in many cases require the intervention of powerful streams from the land. To show where that land was posited, and what was its character, may be an impracticable problem, but it cannot be prosecuted without some indirect advantages, perhaps more than commensurate with the effort which it requires.
The recent work of Mr. Chambers, entitled "Ancient Sea Margins," may be perused with advantage for many examples of old sea and tide river terraces at various stated levels, round a great part of the British shores, and along many of the valleys.
Ancient Valley Formations.
I have some time ago proposed this term, for the ​purpose of combining in one point of view a great number of remarkable ancient phenomena, attesting the former action of water in existing valleys, but flowing at higher levels than the actual stream, unless the land has been raised and sunk. Deposits of gravel at the mouth of a valley, in the form of terraces, abound in most mountain countries (e.g. foot of Glen Roy), on the sides of a valley (as in Tynedale, above Newcastle), at the head of a valley (as at the head of several Cumberland glens).
In Glen Roy, at a very high level, are two parallel lines, or terraces, which run round the mountain sides, and communicate with other drainage streams. The deposit called Löss, on the Rhine, appears of the same nature, so far, at least, as to indicate the deposition of sediments in water flowing at a level many hundred feet above the present River Rhine, and extending beyond what is now its proper valley on the north side of the range of the Ardennes.
In some of these cases there is sufficient proof that the water was not marine, land shells being not infrequently found in the deposits, especially the finer sorts of sediments. The level character of the terraces, which is the most usual form of these accumulations, seems to indicate the existence of ancient lakes at a high level in the valleys where they occur.
Fluviatile Deposits. Upper Terraces. Lower Terraces. Bed of the Valley.
This, however, is less certain than may be commonly imagined; for streams like the rough Arve scatter the detritus brought down from the glaciers over a surface gently declining, as the stream runs, but nearly level in the transverse section. If, by any change of the ​physical conditions, the stream should cut its way to a greater depth, the banks would have that terrace form which belongs to the Lune, the Ouse, the Tees, the Tyne, and many rivers of the North of England. It not uncommonly happens, that two such terraces, at different levels, can be traced for some distance on the sides of a valley, as on the Lune;—occasionally, in the midst of a valley, rises a low hill of gravel corresponding to the lateral terraces. In most valleys, the materials of the terraces are such as the rocks on the sides of the mountains yield; but this is not the case on the Lune about Kirkby Lonsdale, or the Tyne above Newcastle, in both of which situations boulders and gravel from the Cumbrian mountains constitute a considerable part of the deposit. For this reason, they would probably be called diluvial deposits by some writers, and described as raised breaches by others. The confused aggregation of the pebbles, sand, &c. is such as to imply sudden and violent inundations, which delivered a vast body of detritus in a short time, and perhaps followed the line of the valley, but deposited the coarse earthy matters near the sides where the velocity was lessened, as powerful streams are always found to do.
H. W. High water mark.
1. Surface of chalk excavated by water in some ancient period.
2. Surface of ancient tertiary sands, or alluvial sediment left in the chalk valley.
3. Surface of detrital (diluvial) deposit extended over hill and valley.
Existing valleys have, then, in many cases, been traversed by floods of water which have left evidence of their volume, force, and direction. Did they excavate the valleys? or merely follow the traces left by earlier watery violence? Perhaps we must not yet venture to ​propose a general answer to such questions;—there exist, however, cases which bear very decided evidence with reference to them. At a little valley in the chalk of Yorkshire (represented in the diagram, page 4.), which opens to the sea near Bridlington, we behold, as in the above sketch, the solid, laminated chalk, gently declining to the south, excavated in a broad undulation across the laminæ; over nearly the whole breadth of the hollow thus occasioned rests an irregular sandy deposit very much of tertiary aspect; above this, a thick mass of diluvial clay with bouldered stones in great confusion; the whole surmounted, in places, by a widely laminated deposit of chalk and flint gravel. Finally, the channel of the existing little rill is cut, certainly by that rill, in places through the whole series of deposits, into the solid chalk beneath. What does this teach us? First, the excavation of the chalk by an agent which wholly swept away the spoils; secondly, a less turbulent agency introducing sand and gravel, so as partially to fill up the hollow, but not to cover the parts of the chalk beyond; thirdly, a violent impulse of mud and stones brought from a distance over this valley, and the surfaces for miles on each side of it; fourthly, variable but extensive deposits of local gravel; fifthly, the work of the actual stream, which gathered in the ancient hollow.
As we know the chalk to have been raised from the sea, this upward movement may suggest to us the excavation of the rock by oceanic currents, and the partial deposition of sand; the general accumulation of boulders and clay demands a general disturbance affecting other, and even remote, districts; while the mass of chalk flint gravel seems the natural effect of a more local and less violent convulsion. In some instances, local gravel of this description lies both above and below the proper diluvium.
The interval of time here supposed to occur between the original excavation of a hollow or valley in the rocks, and the accumulation in it of the spoils of a violent commotion of water, is indeterminate. So, ​indeed, is that between the cessation of the diluvial floods (whatever they were) and the commencement of the actual stream. Judging from a survey of examples in the North of England, we have no doubt that many of these old river terraces are the remains of estuary deltas accumulated when the sea had wider dominion; and we are strongly impressed with the conviction that it is possible now to point out in certain sheltered spots the pebbly shores which, like the modern Spurn, formed the seaward barrier of these estuaries.
Rock Terraces in Valleys.—There is a peculiar class of terraces in valleys, which indicate in the same manner the successive lowering of the level of descending water (or the successive rising of the land); these terraces are formed by solid rock, with little or no trace of gravel, or other detritus. Such cases are frequent in the mining dales of the North of England, which cut deep into the "Yoredale Rocks" or upper mountain limestone series.
In this varied series of limestone, sandstone, and shale, almost every limestone which overlies shale projects into a terrace; and this sometimes happens to strong sandstones similarly circumstanced. It is easy to see that, as this occurs in many of the branching lesser dales, as well as in the principal valley, it may plausibly be argued that the whole effect is due to atmospheric action. It is probable, however, that this is not a sufficient cause; since additional débris might thus be expected to be falling every day, or, at least, more of this accumulation should remain than we see. We must further observe, that the presumed levels of the water are only clearly marked by continuous terraces when the strata dip nearly in the plane of the valley. It appears, that just as, at this day, a mountain stream crossing the Yoredale Rocks forms waterfalls and cliffs at every ledge of limestone, by the wearing away of the subjacent shales—so the great currents which anciently flowed in the valley ​(whatever they were) excavated the softer strata, and left the hard prominent in terrace cliffs, as in diag. No. 72.
m. Millstone grit summit resting on shales and grits to l, which is limestone, and projects over s, the subjacent argillaceous beds. The same occurs with each lower ledge of limestone l, which, with the gritstone g, usually found beneath, forms a terrace on the hill sides, above a slope of shale.
A different case occurs in valleys which cross and enter deeply into thick masses of red sandstone, such as occurs at Nottingham, Kidderminster, Bridgnorth, &c. At Bridgnorth, for example, occurs a remarkable triple row of terraces on the east bank of the Severn, which appear decisive as to the successive operations by which changes of relative level of the land and the water which excavated the valley were brought about.
Middle Terrace. Lower Terrace."
All the terraces represented in the diagram No. 73. are formed on the face of the thick and easily excavated red sandstone; but it is only on the left (east) bank of the Severn that they are conspicuous, because this is the salient angle,—for it is always observed among the common daily effects of inundations, that such ​terrace-live levels are only marked on the projecting land, while the re-entering angle is excavated to vertical or steep faces.
* ↑ Lyell, in Geol. Proc.
* ↑ Geol. of Yorkshire, vol. ii.