# A Treatise on Geology/Chapter 6, part 4

Fluviatile Deposits.
To discuss fully the origin and history of valleys, is an object reserved for a later section; we may now proceed to consider the effects produced, in valleys already formed, and partially filled with old detritus, by the water running therein. This is a large subject; for, besides the mechanical and chemical actions of the rivers and brooks, which vary according to the hardness and nature of the rocks, there is to be examined the influence of atmospheric vicissitudes, heat and cold, moisture, dryness, frost, &c.; and all the complicated effects thus occasioned are, in relation to the valleys, further modified by the form and slope of the surfaces, the occurrence of lakes, and other circumstances. Streams flowing along a valley under the various conditions which we observe, are to be considered both as eroding and transporting agents; and it is not only conceivable from the admitted instability of the level of land and sea, but perfectly demonstrated by observation, that these seemingly opposite effects have been exhibited at different times by the same river, at the same points of a valley. Moreover, in the course of the changes of level of land and sea, some rivers appear to have quitted their ancient valleys entirely, and to have taken up new courses corresponding to the new conditions; and this, not merely in marshy countries, where a river's course is almost accidental, but in hilly and rocky districts like the vicinity of Ludlow or the borders of Teesdale. It will, therefore, be proper to present as full an account of the phenomena relating to the actual configuration of valleys under different circumstances, as a due regard to reasonable limits will allow. The first thing to be considered is the degree in which the earth's surface is wasted by atmospheric changes and aqueous agency. ​
Waste of the Earth's Surface.
If we consider that the aggregation of rocks and minerals, whether we regard it as a fruit of chemical or mechanical actions, is no otherwise fixed or stable, than as the forces which tend to keep them united are superior to those which from all sides strive to separate them, we shall be prepared to comprehend how the variations of these con stringent and divellent forces, according to heat, moisture, new elementary combinations, &c., bring a silent but sure and often rapid decay on all the structures of man, and on all the mightier monuments of nature, which are exposed to the ever-changing atmosphere. It is painful to mark the injuries effected by a few centuries on the richly sculptured arches of the Normans, the graceful mouldings of the early English architects, and the rich foliage of the decorated and later Gothic styles. The changing temperature and moisture of the air, communicated to the slowly conducting stone, especially on the western and southern fronts of buildings, bursts the parts near the surface into powder, or, by introducing a new arrangement of the particles, separates the external from the internal parts, and causes the exfoliation or desquamation, as Macculloch calls it, of whole sheets of stone parallel to the ornamental work of the mason. From these attacks, no shelter can wholly protect; the parts of a building which are below a ledge, often decay the first; oiling and painting will only retard the destruction; and stones which resist all watery agency, and refuse to burst with changes of temperature, are secretly eaten away by the chemical forces of carbonic acid and other atmospheric influences. What is thought to be more durable than granite? Yet this rock is rapidly consumed by the decomposition of its felspar, effected by carbonic acid gas,—a process which is sometimes conspicuous even in Britain (Arran, Muncaster Fell, Cumberland), but is rapidly performed in Auvergne, where carbonic acid gas issues plentifully from the volcanic regions. ​
Effects of Rain.
Mere rain is a powerful agent of disintegration; and its frequent attacks leave at length, in sandstones and limestones, otherwise very durable, channels of considerable dimensions, which have sometimes been ascribed to other causes. The Devil's Arrows at Boroughbridge, in Yorkshire, are fluted from this cause from top to bottom (except on the under hanging sides, where they cease not far below the summit)—the work of two or three thousand years: and when we turn from these monuments of man to the native crags whence they were cut, "Brinham rocks," and regard the awful waste and ruin there, well marked by the pinnacles and rocking stones which remain in picturesque desolation, it is difficult to avoid indulging a long train of reflection on the processes of decay and renovation which thus seem to visit even the inanimate kingdoms of nature, subjecting all its material elements to continually renewed combinations.
On the broad limestone floors which support the noble mountains of Ingleborough, Penyghent, and Whernside, the rain channels are so abundant as to have attracted the attention of artists and tourists; and on Hutton roof crags, as well as among the limestones of the Alps, they change their direction with the slope of the ground, collect into larger furrows like valleys on a broad surface, and terminate in the large deep fissures, as small valleys often end in a great hollow of drainage. Another remarkable phenomenon of the moorland districts of the North of England, which are formed on the Yoredale series of mountain limestone, may perhaps admit of the same explanation. These are the "Swallow" holes, as they are termed, which range above the outcrop edge of the limestone beds, and act as drainage channels from the surface to the jointed calcareous rocks below. These round or irregular pits and holes are smoothed on the faces and joints of stone, ​as if by the action of acidulated water, the origin of which, from the air or the neighbouring vegetable substances, is not hypothetical.
Effects of Frost.
In no form is the moisture of the atmosphere inefficient in accelerating the disintegration of rocks. Collected in the joints and cavities of mountains, it loosens every thing by its expansion and relaxation; heaped into enormous glaciers on the summits and down the valleys of the Alps, it melts at its lower edges and on the lower surfaces, and thus is ever in motion downwards; augmented from above and diminished from below, its moving masses plough up the solid earth, and, by a wonderful and momentarily insensible energy, pile up, on each side of the icy valley, vast quantities of blocks of stone and heaps of earth, which slowly advance into the lower ground; and these sometimes bear trees and admit cultivation; till, in the course of changes which these rude climates experience, the whole is transported away by the river which flows beneath, and space is left for new augmentations from above. Perhaps no circumstances are so favourable to the collection of materials for rivers to sweep away, as the glacial crown and icy valleys of the Alps, accompanied by the thundering avalanche and frequent landslips, like those of the Rossberg and the Righi. What further happens to these materials belongs to the history of the river.
In modern geological theory, the glacier has become a power not less influential than in other days the diluvial wave; but it is a power in daily action, of which the laws are known and the effects measurable. If, in applying this power to earlier phenomena, we employ larger measures than nature now works by, or stretch our lines in directions where glaciers are now unknown, we are always amenable to the ascertained laws of glacial action. If we may now venture to say these laws are known, let geology gratefully own her obligation to the cultivators of physical science, who ​following the adventurous steps of Saussure, Charpentier, and Agassiz, have, with Mallet, Darwin, Martins, Forbes, and Hopkins, measured, calculated, and imitated the glaciers of many mountains and various latitudes.
Snow is the parent of glaciers; mountains are only their birth-place. Mountain ranges may by their mere narrowness and steepness furnish no cradle; they may be in so dry a region that snows are not abundant, and glaciers grow but feebly, or have such very gradual slopes as to allow of only very slow downward movement. But where the climate favours abundant precipitation of aqueous vapour, on an expanse of high land amidst loftier peaks, from which steep valleys lead down to levels much below the snow-line, the glacier, fed by a perpetual growth from above, and wasted by an eternal corrosion at the lower extremity, is modified by continual transformations of interior substance, and stimulated by a never-ceasing activity of descent.
It is, in fact, a river of ice, slowly winding its way from an inexhaustible upper sea (mer de glace), losing at every instant a part of its substance, and undergoing change in all its features, till, bent, broken, and dissolved, it gives birth to a stormy river, or floats away in icebergs to cool far-distant seas.
The substance of a glacier is not snow, nor is it wholly pure ice; it consists of the peculiar icy compounds, and manifests the peculiar structures which are generated when snow, after partial and interrupted fusion, is re-aggregated by frost. If this fusion be complete, pure ice is the refrigerated result, and this appears in glaciers; but the greater part of the glacial mass is derived from nevé, which is the partially fused and re-aggregated snow. Such being its composition, its parts are not incoherent as snow, nor liquid as water, nor wholly incapable of mutual displacement as solid ice: but it has something of all these properties; for it moves in a coherent mass, which is capable of flexure ​and compression, but when over strained breaks into fissures, and when over pressed is easily crushed. A mass with such a constitution, placed so as to glide down the inclined but very unequal channel of an Alpine valley, may well be expected to present singular phenomena; but these phenomena have not become really known except after long and patient scrutiny by most excellent observers. Saussure has rightly conceived the descent of glaciers to be due essentially to the downward solicitation of gravity; Forbes has measured this descent in different levels of the glacial stream, at different points on its surface, at the same level, at different depths, and in valleys of different characters: Hopkins has made experiments at home, which throw great light on the interrupted or gradual descent of the icy currents. Without pretending to analyse the innumerable memoirs on glacial movement and its geological effects, we may endeavour to sketch the course of a glacier.
Glaciers do not begin to flow from the loftiest peaks of mountains which rise above the perpetual snow-line: there the only downward movement of the snow is by the "avalanche." But in the zone of variable temperature, where the summer melts the surface of the snows which winter had collected, the snowy mass becomes first bathed with water, and afterwards more or less consolidated by frost; it becomes in fact nevé, and, pressed downwards by gravity, begins to glide on its bed, or on surfaces of separation formed within itself, more or less parallel to the local slope of the valley. As we descend below the limit of perpetual snow, the ground, growing warmer, maintains fluidity below the glacier, the descent of which thus becomes less impeded. The glacier moves faster in summer than in ​winter, faster in a warm day than in a cold night, faster in some seasons than in others. Its motion is continual though unequal; faster in the middle than at the sides, and at the surface than in the deeper parts.
The daily motion at a point of the side of the glacier of Montanvert was found by Forbes to be 17.5 inches; and at the centre 27.1: the general proportion of the central to the lateral movement being 1375 to 1000.
In one year the average descent of the Mer de glace was found to be 563 feet. The velocities vary in different parts of the glacier. In the upper part of the glacier above Montanvert 674 feet in a year: lower down 479: at the "Angle," 770: and below Montanvert, 1000.
While thus moving downward, the glacier is subject to enormous waste by the action of sun and wind.
The waste of the glacier above Montanvert is thus given by Forbes:—
| 1842. | 1842. | ft. | ins. | Daily Rate. | Daily Rate. |
| June 26 to | June 30, | 1 | 9 | 4.1 | inches |
| | July 28, | 10 | 11 | 3.6 |
| | Aug. 9, | 14 | 10 | 3.7 |
| | Sept. 16, | 24 | 6.5 | 2.5 |
Thus only a small portion of the mass which quitted the snowy wilds at its source is found to reach the source of the Arve, which, indeed, is formed by a portion of that waste, which is thus indicated.
In the uppermost parts of the glacier some alternations appear of the more snowy and more icy parts of the mass; a kind of stratification. Farther down a peculiar structure, first distinctly described and explained by Professor J. Forbes, appears. This is the veined or ribboned structure, in which laminæ of blue compact ice alternate with other laminæ of ice full of air bubbles, placed in a vertical direction across the glacier. Lower down these plates are no longer vertical, but dip toward the source of the glacier; and they are no longer plane, but curved, so as to present a ​concavity toward the same point. "These alternate bands have all the appearance of being due to the formation of fissures in the aerated ice or consolidated nevé, which fissures, having been filled with water drained from the glacier and frozen during winter, have produced the compact blue bands."
The farther down the glacier we pass the more numerous are the fissures, the more confused the masses of ice which they separate. This arises from the inequality of the bed and sides of the channel; for thus lines of tension are produced, and across these lines of fracture. Very great fissures appear indeed in all parts of the glacier, but the displacements which these occasion as the masses move onward grow more and more remarkable, because of the additional effect of waste on the surface, in the fissures, and below the glacier.
The glacier thus slowly gliding or flowing down its channel is like a huge grinding and polishing mass. Not that the ice of which it consists can wear much even of the limestone and still less of the gneissic bed of an Alpine or Scandinavian valley, any more than pitch can wear hard speculum metal; but the glacier has under it hard stones, which, set as it were in the ice, become as effective agents in wearing away the rock as emery set in the pitch grinds the hardest compound of copper and tin. Nor is it necessary for attrition that the stones should be imbedded; their grinding effect when loose is considerable.
The sides, also, of the glacial valley are worn by similar pressure and similar agency. This is actually seen to be the case at the "angle" on the Mer de glace (Forbes), and in other situations. In fact owing to the circumstance that the glaciers in some seasons extend themselves far beyond their usual flow, and in other seasons retreat within their ancient limits, the scratched, grooved, and rounded rocks which they once covered, and between which they formerly flowed, are visible in many places, and leave no doubt of the power with which glaciers grind their channels. ​
Some of the materials for this grinding are brought down by the glaciers themselves, on which we commonly see, in the middle, or at the sides, or in both situations, sinuous lines of rock fragments, which, being traced up to their source, are always found to be furnished by rocks on the sides or at the junction of glaciers. These streams of stones are called moraine: the lateral streams are furnished by rocks on the side of the flow; a central stream may be formed by the union of two lateral moraines when two glaciers meet and unite, and thus, in the lower part of a glacier, which is formed of many confluent streams of ice, many lines of moraine may be traced. Arrived at the termination of the glacier, these streams lose their individuality for the most part, and constitute a great terminal moraine. Such remain, in many situations, many hundred yards, and even some miles, beyond the present range of the glacier which transported them.
In the diagram (p. 17.) several of the circumstances which have been mentioned are represented. It corresponds to a part of the Mer de glace above Montanvert. Three glacial streams are seen to unite, and three bands of moraine to run down the main glacier (marked m). The figures indicate the number of feet in a year which the glacier moves at the point where they are placed. (From Forbes's Travels in the Alps.)
Amongst the blocks brought down in this singular manner by glaciers, without attrition, are many of enormous magnitude; and, as each moraine band is only fed from certain rocks, it is easy to see that each has its own mineral character, and may bring detritus of a totally different quality from even its next in position. Much more, in this respect, may different glaciers disagree. If then, as in Spitzbergen, on the coast of Greenland, and in Tierra del Fuego, the glacier masses break off in icebergs, it is quite to be expected they should, after carrying their loads of rock to greater or lesser distances, deposit them
Jardin. Lahchaud. Tacul. Lanoire. L'Angle. Montanvert.
combination, just as we see to have been determined by many travellers on the plains of North Germany, Russia, North America, and the regions west and north of the Alps.
The height of the origin of a glacier depends, as already observed, on the elevation of the line of perpetual snow; and this varies, not only with latitude, but by the influence of local causes and peculiarities of climate. In all the northern zone's it is above the isothermal lines of 32, and is so much the more above this line, as the difference between winter cold and ​summer heat is greater. The lower limit of a glacier depends also on local climates, on the abundance of snow, the depth of the glacier, the slope of the valley, and the rapidity of downward motion: for as the glacier is subject to continual waste from atmospheric and terrestrial agency, the longer its course the more is it exposed to this waste. With a long course on a slight declivity glaciers cannot in general descend so far below the line of perpetual snow, as with a shorter course in a steeper glen. In the Alps the steep glaciers of Grindelwald and the valley of Chamouni descend to the level of 5,300 feet below the snow line, while that of the Aar, on an easier slope, reaches only to 2,650 feet. In Norway the glaciers descend 4,400 feet; but in the Pyrenees only 1,700 feet.
The average slope of the whole glacier from the Arveyron to the Col du geant is 8° 52′, and this is nearly the inclination of the upper part. In the middle part, terminating with Montanvert, it varies from 4° 19′ to 5° 5′, and below Montanvert grows so steep as to give measures of 12° and 20° 41′.
The slopes on which glacier movement is possible are of course somewhat less than those which are actually traversed by glaciers, because they are unequal. In some ingenious experiments made in temperatures which allowed the lower surface of a mass of ice to be just losing its solidity, Hopkins has found the following relations between the inclination of the surface on which motion takes place, and the velocity produced. Up to 12° the velocity is uniform.
| Inclination | Hourly Motion in Inches | Inches in 24 Hours |
| 3° | 0.31 | 7.44 |
| 6° | 0.52 | 17.28 |
| 9° | 0.96 | 22.32 |
| 12° | 2.00 |
| 20° | The motion became accelerated. | The motion became accelerated. |
On reducing the inclination to 1° there was still a perceptible movement. This table may be compared with Professor Forbes's measures of the velocities observed in the Mer de glace already given.
Effects of Springs.
Collected in the atmosphere, the rain is filtered through the sandy rocks, passes rapidly by the joints of the calcareous strata, and is stopped by the clays, and by dykes and faults; it then issuing in springs. But it is no longer the same water: rain water is, indeed, far from being in a state of purity; it contains always carbonic acid, frequently some muriatic acid or chloride of sodium, besides other irregular admixtures. In passing through the rocks it absorbs lime, oxide of iron, &c., and on issuing in the form of springs, loses its excess of carbonic acid, and again deposits carbonate of lime, carbonate of iron, &c. From some springs the quantity of carbonate of lime deposited is enormous; with the water of others, sand, gravel, fossil shells, and zoophytic fragments issue. Thus the first operation of water in and upon the earth is the same, viz. to consume away the solid substance of the rocks, and either deposit it in new situations not far from the source, or deliver it to flowing streams to be carried further away.
Springs which have an impeded issue to the surface are the most general cause of landslips: we may
Goldau. ​consider the great fall of the Rossberg as a case of this kind, the water entering and moistening a particular layer of strata, all inclined very highly, so as easily to acquire a descending force, if the cohesion of the parts were weakened by interposed moisture.
The spring, or rather river (Arve), which issues from the foot of the Mer de glace, near Mont Blanc, brings a vast quantity of detritus, which the grinding motion of the glacier on its rocky bed had broken and rolled to pebbles.
Effects of Rivers.
A river thus fed by springs of water not pure, partially filled with earthy matter, flowing with various velocities through soil and among rocks of unequal resisting power, and formed of particles of different magnitude and specific gravity, must exhibit in its long course a great diversity of appearances. Some rocks and soils it may corrode chemically, others it may grind away by its own force and the aid of the sand and particles which go with it: from steep slopes it, must, in general, transport away all the loose materials; but when its course relents, these must drop and augment the land. The finest particles are first taken up and last laid down; the larger masses make the shortest transit.
Rivers, on whose course no lake interposes its tranquillising waters, may be considered as constantly gathering, incessantly transporting, and continually depositing earthy materials. It is, of course, principally in times of flood that they both gather the most materials, and transport them farthest; yet even in the driest season, the feeblest river does act on its bed, wears by little and little even the hardest stones, and works its channel deeper or wider. This it does, partly by the help of some chemical power, from carbonic acid, and other admixtures, but principally by the grinding agency of the sand, pebbles, &c. which it moves along. In times of flood, these act with violence ​like so many hammers on the rocks, ploughing long channels on their surface, or whirling round and round in deep pits, especially beneath a fall, or where the current breaks into eddies over an uneven floor of stone. This is admirably seen at Stenkrith Bridge in Westmoreland, under the waterfalls about Blair Athol, and in North Wales, and, indeed, very commonly. Not infrequently, on mountain sides or tops, far from any stream or channel, phenomena somewhat similar occur, sometimes the effect of rain, sometimes, we may suppose, the remaining evidence of the former passage of running water, when the levels of the country were differently adjusted.
As the slopes are greatest in the upper parts of valleys (generally), and gradually flatten towards the sea, it is commonly observed, that, from all the upper parts of these valleys, rivers abstract large quantities of the finer matter, and in times of inundation, not a little of the coarser fragments of rocks; much of this is deposited in the lower ground, where the current is more tranquil, and generally (unless the river be very deep) slower. We must, indeed, suppose, that every where some wearing effect on its bed ard sides is produced by every river, even to its mouth; but this effect grows almost insensible far from the high ground which gives birth to the streams; and long ere we approach the estuary, the wide flat meadows, which fill the whole breadth of the valley for miles in length, show what a mass of materials has been drifted away from the higher ground. Finally, where the tides and freshes meet, the sediment of both is disposed to drop; and some rivers may be viewed as sending little or no sediment to the sea.
Thus the whole effect of drainage, including all the preliminary influences of the atmosphere, rain, springs, &c., is to waste the high ground, and to raise the low; to smooth the original ruggedness of the valley in which it flows, by removing prominences and filling up hollows; and notwithstanding the length of years that rivers have flowed, they have, in general, net yet ​completed this work: they still continue to add materials to the lower ground, and, in a few instances, to carry out sediment into the sea.
The whole surface of the earth, then, is changing its level, by the mere precipitations of the atmosphere, and their subsequent effects; the high land sinks, and the low land rises; but what is the rate of this progress, we have no complete means of knowing. Few ancient measures of the height of the land which has been wasted, or the area of that which has been accumulated, are worthy of notice; we are, however, sure, from various causes that many valleys have not been altogether worked out by the rivers now running in them; and some natural chronometers have been pointed out by De Luc and others, which rudely limit the length of time during which rivers have flowed, and might be more usefully employed to determine the rate and amount of fluviatile action.
Rivers certainly did not excavate the whole valley in which they flow, for they have not even removed the diluvial detritus brought into them from other drainages, and heaped on the previously excavated rocks.
Rivers have certainly not excavated more than an inconsiderable part of their valleys, for otherwise the Lakes of Geneva and Constance would have been long since filled by the sediments of the Rhone and the Rhine, which issue from these lakes of that lovely hue and transparency which marks their total freedom from all tinge of earthy impurity. When, indeed, we look at the small but growing deltas of the heads of the English lakes, as Derwentwater, Windermere, or Ulswater, and consider the Derwent or the Rothay in its time of furious flood, we shall be disposed to set a high value on De Luc's opinion, sanctioned by Cuvier, Sedgwick, and others, that these deltas prove the comparatively recent date of the present disposition of drainage on the surface of the earth. Rivers flow in certain channels, because these were previously formed by convulsions, and violent movements of water; they ​have exerted all their force in merely smoothing and filling the inequalities of their valleys, and this partial labour they have not accomplished. Will any one, after this, require to be told that rivers did not make their own valleys; and only yield to this truth when, on the chalk and limestone hills, hundreds of valleys are shown him, down which water never runs, and which, indeed, have no trace of a channel?
The upfillings of a valley by the operations of a river ever tend to be formed in horizontal laminæ; or at least their surface is generally level in the direction across the valley, whatever undulations exist beneath, and however rapid may be the longitudinal declivity of the valley. This is well seen in many valleys of the Swiss Jura, the Cotswold Hills, &c.
a. Irregular surface which is the original basis of the valley, b. The sediment left in it, with a plane surface as if deposited in a lake. c. The surface of the valley, uniformly declining among A, the bordering mountains.
When the materials are gravel and coarse sand, deposited by an impetuous stream, the general surface may be level, and yet the laminæ beneath are frequently much inclined, with slopes in various directions, as Mr. Lyell has noticed with regard to the detritus left by the stormy waters of the Arve. The same thing occurs in many of the stratified rocks which appear to have been accumulated under violent agitation near the sea-shore. (See Diag. No. 20. p. 61. Vol. I.)
Lakes on the Course of Rivers.
Plane surfaces existing along the course of valleys, ​are commonly, without further question, supposed to be indicative of the site of ancient lakes, which have been slowly but completely filled: the supposition is often correct, but it is sometimes erroneous. Rapid rivers, which, in times of inundation, drift coarse materials down their rough beds, and deposit them in the expansions of their valleys, are thus partly choked in their courses, and turned into new channels. Thus they wander irregularly over a large area, every where filling it, to about the same height, with a mass of partial deposits, related to the successive positions of the channel, which, when unconfined by man, seeks always the lowest passage. On a cross section of such a valley, these many distinct streams of gravel and sands appear nearly as in the annexed diagram.
But such a distribution of materials appears not to occur in lakes; whether they receive sediments from gentle streams, rapid rivers, or sudden inundations. The reason of this is the great lateral diffusion of motion in water. Where any great depth of quiet water is interposed on the path of a river, the lacustrine sediments assume various modes of arrangement, depending on their own fineness, and the velocity of the water by which they are hurried along.
Deep Lakes on the Course of a River.—On entering a deep lake, the mingled sediment of a river is subjected to a new influence, the descending force of gravity, in addition to the direct horizontal force imparted by the current, and the lateral movements which it occasions. Each particle, in ​consequence, tends to fall from the surface of the water, as it moves forward, or to the right and left of the point of entry of the river, and with an accelerated velocity in the lower part. The path of each particle will be more or less influenced by the direct, lateral, or vertical forces, according to its magnitude and weight. Thus, in the diagram No. 77., which is to represent a vertical section along the path of the river as it enters the lake at the point o, P p p, particles of unequal magnitude,
entering together, describe curves of unequal curvature (they are all related to the same vertical axis, G); the smallest particles being transported furthest, because they have, proportionally, the largest surface, and therefore subside most slowly in the water.
On the horizontal plan (No. 78.) the courses of such deposits are shown to be concentrical, or nearly so, to the point of influx of the river. By such deposits, the Delta of the Rhone in the Lake of Geneva, as well as that of the Derwent in the Lake of Keswick, has been
is found applicable. Returning to the vertical section (No. 77.) we may remark, that the parabolic lines there given, if considered as representing successive depositions, require to be modified above and below: above, by the shifting of (o) the point of influx forward; below, by the circumstance that the curve ceases at a certain depth (n), when it coincides with the line n l, drawn to represent the greatest slope on which the particles will rest. This slope varies somewhat in particles of different size and form. Generally speaking, the structure of these deltas corresponds to the subjoined diagram; where the surface a a′ is level; the lines a n′, a′ n′ are curved, and lie in surfaces of contemporaneous
depositions; and the lines n b, n b′ are straight lines corresponding to the angle of rest in deep water.
We may further observe, that the unequal dispersion of the sediments in water causes another modification of the lamination of such delta. Fine clay is spread far in the water, and settles at length in a general thin deposit over the curved and sloping faces a n b, and on the bed of the lake b b″, after the agitation of the water produced by the inundation has ceased, and the coarser sediment has settled to its place.
If, further, we imagine the waters of such a lake to be calcareous, and liable to slow decomposition, so that layers of carbonate of lime (or shelly marls) are formed, these will be still differently arranged. If the calcareous matter be generally diffused, the layers will not radiate from or collect round a point, but be very generally spread over the bed of the lake; and even when the calcareous substance enters in solution with a particular stream (as often happens), it mixes with the water of the lake so extensively as to yield wider ​and more regular deposits than those produced by merely mechanical agency.
Shallow lakes, subject to fluctuation, produce on the deposits of coarse gravel and sand, which are brought into them by rivers, an effect intermediate between that of deep water and mere fluviatile currents. The conoidal lamination due to the former is complicated with variation of the point of influx arising from the latter; and thus the upper ends of such lakes become irregular in outline, and are filled by insulated subaqueous banks.
New Lands at the Mouths of Rivers.
The deposition of sediments from a river happens in all parts of a valley, even very near to the sources of the stream, if the slopes of the ground permit; but as towards the sea, generally, the inclination becomes the most gentle, it is there that the finer sediments drop most abundantly.
The cross section of the 'straths' or narrow meadows which are produced in the upper parts of valleys are usually level, or rather a little highest near the edge of the river, and a little lowest where the new surface touches the old (technically 'hard') land. The sediment is rather coarser near the river edge, rather finer at a distance from it, but every where laminated according to the frequency and continuity of the inundations.
Inland seas, which by their position are exempt from strong tides and currents, become filled with river sediments, under the same conditions as large lakes. Their area is contracted, by the addition of new land on the margin, and their depth is lessened by the diffusion of fine sediment over the bed, to various distances, according to circumstances already pointed out while treating of lakes.
Some of the most considerable deltas at the mouths of rivers have been accumulated in seas of this quiet character; as the delta of the Nile, which is a continuation of the long valley of Egypt; the wide sediments at ​the mouths of the Po and the Adige, the Rhone, the Danube, and the Volga, and the numerous streams which enter the Gulf of Bothnia. The rate of augmentation of the deltas in the Mediterranean may be determined by comparing the descriptions of ancient and modern geographers; and in some cases verified by roads, embankments, and other monuments of ancient civilisation. Mr. Lyell has collected evidence of this nature in proof of the considerable increase of land at the mouth of the Rhone, since the era of Roman power, and even during the last thousand years. "Notre Dame des Ports was a harbour in 898, but is now a league from the shore. Psalmodi was an island in 815, and is now two leagues from the sea. Several old lines of towers and sea-marks occur at different distances from the present coast, all indicating the successive retreat of the sea, for each line has in its turn become useless to mariners; which may well be conceived, when we state that the Tower of Tignaux, erected on the shore so late as the year 1737, is already a French mile from it."— (Princip. of Geol., book ii. ch. iv.)
Lower Egypt is the gift of the Nile; and Herodotus estimates the sediments borne by the waters of that river to be so abundant, that if diverted into the Arabian gulf (Red Sea), they would fill it up in 20,000, or even 10,000 years. But the further growth of the great Nilotic delta is checked by a powerful littoral current, which washes the African coast from Gibraltar to Egypt. The accession of new land on the coasts of the Adriatic is perfectly known, since the Augustan days of Rome, and the rate of increase is inferred to have been even augmented during the last 200 years. For by Prony's account (Cuv. Disc, sur les Rev. du Globe), the shore was 9000 or 10,000 metres from Adria in the twelfth century; 18,500 metres in the year 1600; and between 32,000 and 33,000 metres at present; which gives an average yearly increase of breadth of new land of 25 metres from 1200 to 1600, and 70 metres from 1600 to 1800. This augmentation may ​probably be ascribed partly to the shallowing of the whole upper end of the Adriatic, and partly to the alterations of the system of internal drainage, whereby the rivers, enclosed in extensive embankments, are prevented from depositing much of their sediment upon the ancient alluvial lands. "From the northernmost point of the Gulf of Trieste, where the Isonzo enters, down to the south of Ravenna, there is an uninterrupted series of recent accessions of land, more than 100 miles in length, which within the last two thousand years have increased from ten to twenty miles in breadth."—(Lyell, book ii. ch. iv.)
The surfaces of deposition from rivers thus entering quiet seas are in general inclined at a very moderate angle: at the mouth of the Rhone the water deepens gradually from four to forty fathoms, in a length of six or seven miles ($\scriptstyle {\frac {32}{5720}}$), or 1 in 160, a "dip" less than the average inclination of our so-called "horizontal" strata. Reasons are assigned for adopting the opinion that the Adriatic, now so shallow, was once a deep sea; if so, the sediments on its bed, raised into dry land, would constitute a modern formation equal in importance to a large part of the subapennine tertiaries, and, according to the testimony of Donati, very similar to them in mineral composition, and the arrangement of their organic contents. The sediments consist of mud and calcareous rock, with shells grouped in families, as we often find, them in ancient strata. The deposits from the Rhone are ascertained to be in a considerable degree calcareous, sheets of limestone indeed; and the mud of the Nile contains nearly one half of argillaceous earth, about $\scriptstyle {\frac {1}{4}}$th of carbonate of lime, and $\scriptstyle {\frac {1}{10}}$th of carbon, besides silica, oxide of iron, and carbonate of magnesia. (Girard, quoted by Lyell.) Materials of this description may be deposited together; but little doubt can exist that, during their solidification, the arrangement of the particles may be so influenced by peculiar attractions, as to exhibit many of the circumstances noticed among old sedimentary rocks, as concretions of ​limestone, siliceous nodules, segregations of oxide of iron, &c.
These recent deposits sometimes are laminated like the old rocks. De Luc notices, near Groningen and Enckhuysen, the division of the silt deposit into layers, by the annual growths of grassy turf buried in sediments. At Enckhuysen, he also observed between the layers ("couches") of sediment, sand and shells, and very justly calls attention to the value of this example of the different effects which may be occasioned by currents in the modern ocean, comparable to the appearances in the solid crust of the globe. (Lettres sur l'Histoire de la Terre et de l'Homme, vol. v. p. 289.)
The general result of atmospheric and fluviatile action is to equalise the levels of the land, to smooth and mask the original inequalities of the surface, partly to deepen, but principally to elevate the valleys. The sediments which remain on the course of rivers, are all more or less inclined, and thus, from their sources down to the sea, and into the sea, a series of inclined deposits, pebbly, sandy, argillaceous, and calcareous, may be always observed. These deposits are subject to much irregular wasting, by inundations and change of the river channels, while unconfined by art; when embanked, a new order of phenomena arises.
In rivers whose mouths are carried farther and farther continually into the sea. the moving force of the stream would be lost, did not the level of the water rise between the sea and the upland. In a state of nature, this may be sometimes accomplished by successive depositions of sediment over all the parts of a large surface; but there are many cases in which it is evident that rivers tend to embank themselves, by depositing along the sides of their channels a greater proportion of sediment than falls elsewhere. This effect is most striking along streams which bear gravel and coarse sand, as near Kirkby Lonsdale, and in all mountainous countries. Rivers which are forced by artificial barriers to flow in one channel, across a flat alluvial tract, to the sea, ever ​tend to raise their own beds, and the embankments, rising with them for the protection of the marshes, exhibit in the Po and the numerous rivers of Holland, and the English fens, the singular spectacle of vase volumes of water, flowing on levels many feet or yards above the cultivated fields, and even higher than the houses, which are often placed below the shelter of the dangerous bank. Hardly any thing can be imagined more awful than the bursting of river banks in the fen lands of Norfolk, Cambridgeshire, and Lincolnshire.
Estuary and Shore Deposits.
Rivers which discharge themselves into the ocean, where tides and currents break with a certain regularity the quiet of its waters, exhibit always at their mouths, and often along the lower part of their channels, another set of phenomena.
Where the tide enters a river's mouth, and periodically combats the freshes, these are "backed" to certain distances, their motion is nearly destroyed for a time, and the sediment, which was only suspended by the agitation of the water, is dropped in the interval of quiescence. The stronger the current from the land, the further toward the open sea are its sediments carried, so that in many cases large quantities pass beyond the estuaries and float away on the heavier salt water, even to hundreds of miles from the coast. (Vol. I. p. 342.)
It is easy to perceive that, by this process, every river connected with a tidal sea is continually repelling the salt water, and making new land by its fresh-water deposits. Thus it happens that many towns to which the tide formerly reached, in the days of Roman sway, as Ribchester, Norwich, York, are now wholly or partially deserted by it, and large breadths of marsh land occupy the sites of ancient tide lakes. It is, however, true, that the tide waters themselves have contributed some part of the sediment which forms the wide marsh lands by the Thames and the Medway, the enormous breadths ​of fen land in Lincolnshire and Cambridgeshire, and the warp or silt lands on the Trent, Aire, Ouse, and Derwent. The latter cases are very instructive, because, by studying in connection the operation of the sea on the coast of Holderness, and in the tributaries of the Humber, we see very plainly an important benefit arising from the enormous waste of that ill-fated coast (2¼ yards per annum for 30 miles from Kilnsea near Spurn Point to Bridlington). The mean height of this wasting cliff being taken at only 10 yards, the total quantity of fine sediment, coarse sand, pebbles and boulders, falling into the sea in one year = (1760 x 30) X (10x2¼) = 1,188,000 cubic yards. Now, though not all this mass of sediment must be supposed to enter the Humber, a considerable portion of it does, and is turned to good account by the industrious and intelligent inhabitants, in the practice of warping. This consists essentially in admitting the muddy waters of the tide at its height, and especially in spring tides, to flow through proper channels over the low land adjoining the rivers, so that by stagnation it may drop its sediment, and again be returned to the Humber. By frequent repetition of this simple process, the hollow places near the rivers which are connected with the large estuary of the Humber are filled up, and thousands of acres of land raised in level one foot, or eighteen inches; and by the addition of most excellent soil augmented in value from a mere trifle to above the average of the country. The annual waste of the Holderness coast alone would cover to the depth of one foot 3,564,000 yards, or about 737 acres. It is often imagined that all the "warp" of the Yorkshire rivers descends with the fresh waters: this is so far from the fact that it is in dry seasons, when the freshes which bring no sediment do not dilute the rich tide water, that the process is most successful. The quantity of sediment contained in the water in a dry summer is great, and chokes the channel of the Dun about Thorne; but in winter the floods clear it away. ​
The water of the Rhine transports, according to Mr. Homer's experiments at Bonn, about $\scriptstyle {\frac {1}{16000}}$th part of its own volume of mud; and the extent of alluvial land, at the mouth of this and other German rivers which enter the North Sea, shows that in some earlier times the conditions of that sea were such as to favour accumulation, and permit of secure embankments. But, for some hundreds of years, a different scene has been presented; both natural and artificial barriers have yielded to the increased pressure of the sea, large tracts of the main land are lost in the waves, while the islands that still fringe the coast, relics of a once continuous tract, have been diminished, and are still undergoing waste. In 1421, the wide surface of the Bies Bosch was overwhelmed; in the thirteenth century the Zuyder Zee was excavated; and since the year 800, Heligoland, with other islands, has been nearly swept away; and, from Belgium to Jutland, the whole coast has more or less changed its form in consequence of the incessant attack of the sea. The history of Nordstrand and other islands belonging to Sleswig, formed of alluvial land, which was deposited, fortified, and afterwards devastated by the sea, as given by De Luc (Geol. Travels, vol. i.), is extremely instructive, and places in a clear light the contrast between what may be termed the ordinary processes, whereby sediment is accumulated, and the extraordinary and wasteful violence of the North Sea when swollen by high tides, and urged by powerful north-westerly winds.
By Capt. Denham's survey of the estuary of the Mersey, it appears that a cubic yard of water of the flood tide holds 29 cubic inches of mud in suspension, and a cubic yard of water of the ebbing tide 33 inches; and the quantity of water moving up and down is such, that with every ebb tide 48,065 cubic yards of sediment pass out of the estuary, and are detained by the banks outside the Rock Narrows, excepting that part which the succeeding ebb tide disturbs. The excess of silt thus accumulated from 730 refluxes of the year's ​tides amounts to 35,087,450 cubic yards; and the annual tangible deposit over a certain area (allowance being made for shrinking to half its bulk) is estimated at 11,695,817 cubic yards. The cross set of the Irish Channel currents limits the extension outwards of the shoals.
The proportion of sediment thus found in the Mersey (33 cubic inches in a cubic yard = $\scriptstyle {\frac {1}{1414}}$, and 4 cubic inches the quantity really deposited = $\scriptstyle {\frac {1}{11664}}$,) may perhaps exceed the average for British estuaries, but is much below some estimates, or rather conjectures, collected by Mr. Lyell, from Rennell, Sir G. Staunton, and others. Mr. Everest found in the water of the Ganges, during rains, $\scriptstyle {\frac {1}{856}}$th of its volume of mud; and the total annual discharge of sediment into the Bay of Bengal 6,368,077,440 cubic feet (= 235,854,720 cubic yards). (Biblioth. Universelle, 1834). In the Severn Mr. Ham found on an average 40.3 grains of sediment in an imperial gallon of water, weighing about 10lbs., or 70,000 grains—proportion of weight as 1737 to 1: of bulk as 6948 to 1 nearly. (British Association Reports, 1837.)
If researches of this nature had been prosecuted in various quarters of the globe, and on rivers flowing over different classes of rocks, the results would have been of great value in geological reasoning.
If the country drained by the Ganges is 300,000 square miles, its average waste, from Mr. Everest's data, would appear to be 78.6 cubic yards per square mile of 3,097,600 square yards, = $\scriptstyle {\frac {1}{4000}}$ of a yard in depth, which is about $\scriptstyle {\frac {1}{111}}$th of an inch per annum from the whole surface of drainage! In 8000 years this would be equal to the mass of the English tertiaries, assumed to be on average 800 feet thick, and to have a surface of 6000 square miles. The Brahmaputra is supposed to discharge as much sediment as the Ganges.
On the narrow bed of the quiet Adriatic we behold the accumulation of conchiferous mud, hardly different from the subapennine tertiaries which have formerly been ​raised from out of the Mediterranean; in the wider Bay of Bengal the diffusion of river sediments is complicated by tidal action and periodical winds; and the North Sea gives us in addition, all the variations of opposing and concurrent tides, entering from opposite points, and diverted into a variety of channels by the form of the coast and the inequalities of the sea bed. How various are the materials therein deposited! Boulders of granite and other rocks, drifted from the Cumbrian mountains, fall from the Yorkshire cliffs, mixed with oolitic limestones, and chalk and flints; blocks of Scandinavian rocks are mixed with the silt along the coasts and islands of Denmark; the Thames brings tertiary, the Tees secondary, the Dee primary detritus. And all these ingredients, distributed over the shallow bed by violent currents and storms, mix with volcanic sediments from the Rhine, cretaceous mud from the English Channel, and organic exuviæ drifted from the polar circles, or perhaps brought by the gulf stream from the tropical shores of America.
This remarkable sea bed is so nearly level, that its slight inequalities are indiscernible when drawn to a true scale, yet it is really channelled and undulated, and liable to change in the form of its surface, since we are informed that currents have cut through Heligoland a channel 60 feet in depth.
Upon such a surface some organic bodies will be entombed entire, where they lived and as they died, (oyster-beds for example, comparable to the fossil oyster beds in the oolitic system,) others will be displaced, and floated to various distances, and deposited in unequal states of imperfection. Some bivalve shells will be found in the rocks which they have bored, others with valves just held by the ligament, or widely separated, or broken among pebbles; fishes entire, or disintegrated; their scales and teeth drifted away by the currents, and mixed in various combinations with the unsettled sediments.
Now, most or all of these circumstances may be paralleled among many of the strata; especially among ​the tertiary and certain parts of the oolitic systems of strata; and a benefit would be conferred on geology if a careful and accurate survey were made of the mineral and organic contents of the whole bed of the German Ocean, for which object its shallowness (it nowhere exceeding 30 fathoms in depth between the Humber and the Elbe) offers unusual facilities.
Lacustrine Deposits.
Until the publication of Cuvier and Brongniart on the Environs of Paris, the attention of geologists was but feebly turned to the study of the numerous fresh-water deposits, from which, chiefly, we are to learn the ancient condition of the land, as the stratified marine sediments give us information of the contemporaneous operations in the sea. The general scale of geological time most certainly is founded on the series of marine deposits; but our views of the changing conditions of the globe will be very imperfect if we are not able to arrange on the same scale the monuments which remain of the contemporaneous operations on the land.
At certain points in the series of tertiary strata this can be done with certainty, or probabilities of various value, by the legitimate process of observed interstratification. Marine post-tertiary deposits are sometimes associated with lacustrine sediments, in such a manner as to determine a few points of union in times approaching our own day.
But, for a very large proportion of lacustrine formations, the important data of interposition among marine strata are wanting, and we are only able to affirm that the fresh-water sediments are of a date posterior to a certain marine formation, because they rest upon it.
Some few of these lacustrine formations can, by some monuments of art and civilisation, be proved to belong to the period since the creation of man, or even be limited within certain historical dates; but there remains a large class of desiccated lakes whose antiquity must ​remain indefinite, both as regards the historical and geological scales of time, unless we can find tests independent of successive deposition, and of remains of human art, and yet comparable with natural monuments both in the ancient and modern, the geological and the historical, ages of the world.
These are the organic remains of plants and animals; and before employing their powerful and abundant testimony in solving the difficulties which attend a classification of lacustrine deposits, we must be satisfied on two points.
1. That faithful observation and correct inferences have established the fact that to every successive geological period belonged characteristic groups of marine plants and animals, which, in every region yet explored, may by comparison of selected genera and species, be discriminated from marine groups of earlier and later date, whose remains are buried in that region.
2. That through the whole series of strata, the organic productions of the land and fresh water, which are mixed with or interposed in beds among marine strata, present variations of form and structure similarly related to geological time.
On these points the reader who consults Vol. I. chap. v. of this work, and considers the drawings and notices of the organic remains of the several systems of strata, will probably need no farther proof, except what the following investigation may yield. There remains, then, only the difficulty of deciding how far the relics of plants, shells, fishes, reptiles, and quadrupeds, which occur in the lacustrine sediments of all ages, are sufficiently numerous and characteristic to justify positive inferences. This must be left to the judgment of geologists in each particular case, attention being always directed to the circumstances which accompany the inhumation of terrestrial and aquatic beings in the present condition of nature; for it is very certain that only a small proportion of land or fresh-water plants, ​molluscous, articulated, or vertebral animals, is entombed in lacustrine sediments.
Purely lacustrine deposits are almost unknown among any of the stratified rocks of earlier than tertiary date. The laminated carboniferous limestones of Burdie house, near Edinburgh, can hardly be admitted an exception, any more than the calcareous beds of Ardwick and Lebot wood, which lie nearly at the top of the coal formation of England. These deposits may indeed be thought to mark the influence of fresh water predominating over that of an estuary, such as we suppose to have received the sediments and vegetable relics which constitute the coal formation above millstone grit.
Fresh water products again appear in the midst of the oolitic strata of Yorkshire, accompanied by circumstances almost perfectly comparable to those which characterise the true coal formations; the same fact is repeated in the strata of the Wealden; tut in each of these instances the observers most attentive to the phenomena have decided that they indicate fluviatile not lacustrine accumulation. The argillaceous and calcareous strata of Purbeck and the upper Wealden beds certainly come nearer to the notion of quiet sediments, collected in a lake, than any other deposits of secondary or earlier date.
It is therefore very interesting and important to study with care and perseverance the varied mineral characters of the supracretaceous lacustrine sediments; and to compare the organic contents of those whose place on the scale of marine strata is known, in order to obtain rules for judging of the relative age of others which are less favourably circumstanced. Some of the results of this study we propose to exemplify, in the following brief notices of remarkable lacustrine formations.
Upon a general review of the ossiferous deposits of Europe, we discover two very distinct assemblages of animal remains, belonging to two obviously distinct and widely separated geological periods, both anterior to the ​completion of the present arrangement of organic life, and main features of physical geography in these regions; viz. the eocene or lower tertiary mammalia and the animals of the diluvial period. Between these two groups, are many assemblages of intermediate character, and intermediate geological position (as in Touraine), and later than all of them are other deposits which (imperfectly) unite the diluvial to the existing fauna. The mammalia whose remains lie in the lower tertiary rocks may be considered as having lived on the land previously to the origin of these strata; and those whose relics fill caverns and gravel-beds obviously belong to a surface of the earth which has been modified by subsequent revolutions. We have therefore the following general classification of the results arrived at in studying fossil mammalia:—
| Modern period | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | Pachydermata almost lost; ruminant quadrupeds assume preponderance, as stag, ox, sheep, &c. wolf. |
| Diluvial era | $\left\{{\begin{matrix}\ \\\\\ \end{matrix}}\right.$ | Pachydermata abound, mostly of living genera; as mammoth, hippopotamus, rhinoceros, tapir, horse, pig; large feline and bovine quadrupeds and deer abound. |
| Tertiary period | $\left\{{\begin{matrix}\ \\\\\ \end{matrix}}\right.$ | Pachydermata of extinct and living genera abound; as mastodon, hippopotamus, rhinoceros, dinotherium, anthracotherium, horse, deer; feline quadrupeds not rare. |
| Supracretaceous era | $\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.$ | Pachydermata of extinct genera first appear, especially palceotherium, anoplotherium, lophiodon. |
| Secondary period | $\left\{{\begin{matrix}\ \ \end{matrix}}\right.$ | Marsupial quadrupeds occur in one place (Stonesfield). |
Mr. Lyell's classification of tertiary strata (vol. i. p. 267.) may be easily reduced to this scale, with sufficient accuracy for our present purpose, by reading for diluvial, newer pleiocene (according to the tendency of book iv. ​chapter xi. of the Principles of Geology), for supracretaceous eocene, and by uniting the meiocene and older pleiocene periods. Upon this basis it appears worth while to inquire how far the shells found in lacustrine sediments support the inferences of the change of organic life, since the age of the chalk, which have been drawn from marine remains and bones of terrestrial quadrupeds, though there is reason to regret the neglect which this important subject of research has experienced. Contemporaneous with the marsupials of Stonesfield, and with the extinct dinosaurians of Sussex and Yorkshire, we have freshwater shells in the oolitic coal series of Whitby (Unionidæ) and others of like affinities in the Wealden beds. A valuable addition to our knowledge of the lacustrine deposits of Purbeck has lately been given by Professor E. Forbes. These truly lacustrine beds rest without gradation on the truly marine beds of the Portland oolite. These lowest freshwater beds contain modern genera, viz., cyprides, valvata, limnæa; above them are the well-known dirt beds with the bases of cycadeæ in situ; above the dirt beds are cypridiferous shales, covered by a varied series deposited in brackish water, and containing rissoæ and protocardia, and serpulites. Over these come again purely freshwater beds marked by cypris, valvata, and limnæa. Then a thin marine band,—followed by another group of freshwater beds with cypris, valvata, paludina, planorbis, limnæa, physa, cyclas, all different from their conveners in the beds below. With them are some vesicles of chara (gyrogonites). Marine beds cover these, and are followed by beds of freshwater and brackish origin, with the same cyprides as below, some fishes, &c. Again marine beds and brackish beds, and a third series of freshwater strata with a new series of fossils, cyprides, paludina, physa, limnæa, planorbis, valvata, cyclas, unio,—all modern genera. Marine strata come on above. ​
"So similar are the generic types of these mollusca to those of tertiary freshwater strata and those now existing, that had we only such fossils before us and no evidence of the infra position of the rocks in which they are found, we should be wholly unable to assign them a definite geological epoch." In the lapse of time during the deposition of these Purbeck strata, there was no great physical disturbance there, nor were the sediments much varied in mineral character, nor were the generic forms changed, and these forms are yet continued in other species which are in existence at the present day in the same physical region. The scale of lacustrine life, if formed on the mollusca, would not be marked by generic steps, as the contemporaneous scale of marine life is. Perhaps we may admit a similar result in the case of aquatic and land insecta, as compared with marine Crustacea.
Eocene, or lower tertiary Period.
The freshwater sediments of the Paris basin, studied in connection with those of Auvergne, Velay, and Cantal, offer a very complete view of the eocene lake deposits, and lead to the conclusion that the marine and freshwater strata of that basin are to be considered as marking sometimes the independent action of the sea and land floods in one basin, and sometimes their periodical alternation; the land floods always coming from the south, and the marine sediments from the north or west.
The gypseous deposit of the Paris basin is a repository of many extinct species of quadrupeds, while of birds 10 species, and several fishes and reptiles, also extinct, remain to augment the value, and complete the evidence presented by these precious relics. Four fifths of the quadrupeds belong to the division of pachydermata; and nearly all the species are such as might be supposed ​habitually to frequent the margins of rivers and Jakes. Among them are
Cheiroptera, Vespertilio Pariensis.—Carnivora', Nasua; Viverra Parisiensis, and 2 others; Canis, 2 species.— Marsupiata, Didelphis Cuvieri, and another.—Rodentia, Myoxus, 2 species; Sciurus.—Pachydermata, Adapis Parisiensis; Chæropotamus Pariensis; Anoplotherium commune, A. Secundarium; Xidophon gracile; Dichobune leporina, D. murina, D. obliqua; * Palæotherium magnum, P. medium, P. crassum, P. latum, P. curtum, P. minus, P. minimum, P. indeterminatum; Lophiodon———.
Among the reptiles are trionyx Parisiensis, emys (several species) crocodiles.
Palms and other endogenous plants accompany these remains.
In this list of undoubtedly eocene quadrupeds, we remark, with interest, first, the total absence of ruminant animals; secondly, the great predominance of the pachydermata; thirdly, the deficiency in this group of the elephant, rhinoceros, hippopotamus, mastodon, and horse; and, fourthly, the deficiency of large feline beasts. By all these characters the eocene deposits differ widely from those which have been generally called diluvial.
The quarries of Binstead, and cliffs near Ryde, have yielded to Mr. Pratt, Mr. W. D. Fox, and Mr. W. V. Harcourt, bones of palæotheriu, anoplotheria, chæropotamus, and perhaps dichobune, as Mr. Owen has recently stated to the Geological Society (Proceedings, Nov. 18, 1838). The species are
| Palæotherium medium | Anoplotherium commune. |
| ——————— crassum | ——————— secondarium |
| ——————— minus | Chæropotamus —————. |
| ——————— curtum | Dichobune ? (This was formerly described as a species of moschus.) |
| ——————— a new species | Dichobune ? (This was formerly described as a species of moschus.) |
The agreement of this list with that of the animals of the corresponding beds in the Paris basin is remarkable. ​
All the land and fresh-water shells of the basins of Paris and Hampshire belong to extinct species. In Hordwell cliff' Mr. Lyell found viviara lenta, melania conica, melanopsis carinata, M. brevia, planorbia lens, P. rotundatus, Limneæa fusiforrnis, L. longiscata, L. columellaris, potamidutn margaritaceum, neritina, ancyhis elegans, unio solandri, mya gregarea, M. plana, M. subangulata, and 2 species of Cyclas. (Geol. Trans. 2d Series, vol. ii.)
The coeval beds of the Paris basin contain Cyclostoma mumia; Limnæa longiscata, L. elongata, L. acuminata, L. ovum, bulimus pusillus, &c.
Middle Tertiary Period.
In the upper fresh-water beds of the Paris basin (considered eocene by Mr. Lyell) occur many shells closely approaching recent species, as well as those of the true palæotherian age. The series is cyclostoma truncatum, C. elegans antiquum; Potamidum Lamarckii, Planorbis rotundatus, P. cornu, P. prevostinus; limnæa cornea, L. fabulum, L. ventricosa, L. inflata, L. cylindrus; Bulimus pygmæus, B. terebra; paludina carinata; Pupa Defrancii, P. muscorum; Helix lemana, H. desmarestina.
In the fresh-water limestone of Saucats, near Bordi aux (considered to be of meiocene date by Mr. Lyell and M. Deshayes, but ranked with later deposits by M. Dufrenoy,) are found Cyrena Brongniarti, Planorbis rotundatus, and Limnæa longiscata.
A strong analogy to existing as well as extinct species appears in the fresh-water deposits of Aix in Provence, where, according to Lyell and Murchison, the series of strata in descending order is as follows:—
150 feet of white calcareous marls and limestone, calcareous and siliceous millstone and resinous flints,—containing Potamidum Lamarkii, Bulimus terebra, B. pygmæa; Cyclas gibbosa, and another species.
The subjacent strata (marls, with fishes, plants, &c.) run out into a terrace, beneath which gypsum is ​extensively worked. "In this upper gypsum fossil insects occur exclusively in a finely laminated bed of 2 inches in thickness: still lower are two other ranges of gypsum, the upper one of which alone is worked; the marls associated therewith contain nearly as great a quantity of fishes as those of the upper calcareous zone. Beneath these are beds of white and pink coloured marlstone and marl, inclined at 25° to 30°, containing Potamidum Lamarckii, and Cyclas aquæ Sextiæ; and these pass downwards into a red sandstone and coarse conglomerate. The fundamental rock of the whole district is a secondary limestone, with belemnites, gryphites, and terebratulae." In the contemporaneous lignites of Faveau, Planorbis cornu, P. rotundatus, Melania scalaris, cyclades, and a unio occur; thus rendering the resemblance of the testacea of this deposit to those of the Upper Parisian freshwater beds very striking.
The insects of this deposit consist of Coleoptera 20 species, Orthoptera 8, Hemiptera 20, Neuroptera and larvæ, Hymenoptera 8, Lepidoptera 2, Diptera 15; there are also Arachnida. In the opinion of Marcel de Serres and Curtis, they are almost entirely included in genera now living in the south of Europe; and several species, as Brachycercus undatus, Acheta campestris, Forficula parallel, and Pentatoma grisea, are supposed to be identical with living types.
The freshwater beds of Alhama yielded to colonel Silvertop—
| Planorbis rotundatus of the Isle of Wight. | Paludina desmarestina. |
| ——————— new species. | ——————— pyramidalis. |
| Bulimus pusillus. | Ancylus. |
| Paludina pusilla. | Cypris. |
| | Limnæa. |
And at Teruel. Aragon, occur—
Limnæa pyramidalis.
In the freshwater beds of Cantal, according to Lyell and Murchison, are found—
Limnæa acuminata, L. columellaris, L. fusiformis, L. longiscata, L. inflata, L. cornea, L. fabulum, L. strigosa, L. palustris antiqua.
Bulimus terebra, B. pygmæus?; B. conicus.
Planorbis rotundatus, P. cornu, P. rotundus.
Ancylus elegans.
At Montabusard, a league west of Orleans, in marls with Limnæa and Planorbis, at a depth of 18 feet, bones of land mammalia were found, belonging to cervus, rhinoceros, mastodon tapiroïdes, palæotherium, and lophiodon. The deposit is thought to be younger than the millstone freshwater beds of Paris. In freshwater beds in the Orleannois, are found Mastodon angustidens, M. maximus?; Hippopotamus, Rhinoceros incisivus, R. minutus, Dinotherium giganteum, Canis, 2 rodentia, and 1 ruminant.
Lacustrine deposits of undoubtedly meiocene age are scarcely known;—the list of quadrupeds of this period must therefore be chiefly collected from the marine beds of Touraine, Bourdeaux, Dax, &c.
In the marine beds of Touraine, the following mammalia are found:
| Mastodon angustidens. | Anthracotherium. |
| Hippopotamus major. | Palæotherium magnum. |
| ——————— minutus. | Equus. |
| Rhinoceros (large). | Lepus. |
| ————— minutus. | Cervus, 2 species. |
| Dinotherium giganteum. | |
If this list be compared with that of the Paris basin, we perceive, that mastodon, hippopotamus, rhinoceros, dinotherium, anthracotherium, and equus, are introduced among the pachydermata, but without excluding the palæotheria, and that ruminant quadrupeds appear.
At Eppelsheim, on the Rhine, the sandy deposit has yielded a large suite of animal remains, now in the museum at Darmstadt, which present a general analogy to those of Touraine, but possibly are of somewhat later date. Among them are—
| Carnivora | — | Gulo antediluvianus. |
| | | Felis aphanistes. ​ |
| | | Felis ogygia. |
| | | —— prisca. |
| Rodentia | — | Palæomys castoroides. |
| | | Aulacodon (Chelodus) typus. |
| | | Chalicomys Jageri. |
| | | Spermophilus supercilious. |
| | | Myoxus (Arctomys) primigenius. |
| | | Cricetus (vulgaris?) fossilis. |
| Ruminantia | — | Moschus antiquus. |
| | | Cervus anocerus. |
| | | ——— brachycerus. |
| | | ——— trigonocerus. |
| | | ——— dicranocerus. |
| | | ——— curtocerus. |
| Pachydermata | — | Rhinoceros Schleiermacheri. |
| | | ————— incisivus. |
| | | ————— leptodon. |
| | | Mastodon angustidens. |
| | | ———— arvernensis. |
| | | Equus caballus primigenius. |
| | | —— mulus primigenius |
| | | —— asinus primigenius. |
| | | Tapirus priscus (Lophiodon Cuv.) |
| | | Lophiodon Goldfussii. |
| | | Sus antiquus. |
| | | —— palæochaerus. |
| | | Dinotherium bavaricum. |
| | | —————— giganteum. |
| Edentata | — | Manis gigantea. |
At Georges Gmünd, near Roth, beds of sandy marl and whitish concretionary limestone crown low hills of keuper sandstone, and contain subordinate beds of calcareous, ferruginous, and bony breccia.
The catalogue of the bones found at this place by Count Munster and other observers, is thus given by Meyer (Palæologica, 1832):—
| Mustela, new species. | Dinotherium bavaricum. |
| Ursus spelæus. | Lophiodon, 2 species. |
| A new species of carnivore. | Palæotherium magnum. |
| Mastodon angustidens. | ——————— aurelianense. |
| ————— arvernensis. | Anthracotherium. |
| Rhinoceros tichorhinus. | Cheeropotamus Sommeringii. |
| ————— incisivus. | Cervus. |
In Mr. Murchison's account of Gmünd (Geol. Proc. ​1831), it is said that Mr. Clift has also identified fragments of the teeth and bones of the hippopotamus and ox. From these data the deposit of Gmund appears to belong to the middle part of the tertiary series.
The slaty marls and limestones of Oeningen, some of them bituminous and fetid, which rest upon the "molasse" of the Rhine valley, contain plants, insects, one shell, numerous fishes, some reptiles, and mammalia, of which the following is a synopsis, from Meyer, Murchison, &c.
| Mammalia:— | |
| Vespertilio murinus? v. fossilis. | Leuciscus pusillus, heterurus. |
| Vulpes fossilis. Mantell. | ————— oeningensis. |
| Mus musculus fossilis. | Tinica leptosomus, fuscata. |
| Myoxus. | Aspius gracilis. |
| Lagomys. | Rhodius latior, elongates. |
| Anoema oeningensis. König. | Gobio analis. |
| Reptilia:— | Cobitis centrochir, cephalotes. |
| Chelydra serpentine. Bell. | Acanthopsis angustus. |
| Salamandra gigantea. | Lebias perpusillus. |
| Triton palustris? | Esox lepidotus. |
| Rana. | Perca lepidota, |
| Bufo. | Cottus brevis. |
| Fishes (Agassiz):— | Anguilla pachyura. |
Mr. Murchison's examination of Oeningen led him to believe that it was to be referred to one of the most recent tertiary aeras (Geol. Proc. vol. i. p. 169 and 330.): but M. Agassiz, finding all the numerous fishes of this deposit to be of extinct species, regarded it as of higher antiquity than was generally supposed; and as both the tortoise (chelydra serpentine Bell) and the fox are extinct species, while the analogies offered by the insects, plants, &c., are in most instances merely generic, this may prove the most satisfactory conclusion.
| Insecta | — | Formicidæ, hymenoptera, libellulidæ. Anthrax, cimex, coccinella, blatta, vespa. |
| Mollusca | — | Anodon Lavateri. Al. Brong. |
| Plants | — | Fraxinus rotundifolia? Lind. Acer opulifolium? a. pseudoplatanus? Populus cordifolia. |
Lakes of the Pleiocene and Diluvial Period.
In this series of deposits, we hardly ever meet with limestone strata, comparable to those of older date; there are sometimes about the accumulations such considerable marks of local violence of water, as to render it doubtful whether the bones and shells have not been drifted from other situations. The löss beds of the Rhine probably belong to this period.
In the newer pleiocene deposits of the valley of the Elsa in Tuscany, which consist of several hundred feet of marl, and shelly t raver tins disposed horizontally, six living species of testacea were recognised by M. Deshayes: viz. Paludina impura, Neritina fluviatilis, Succinea amphibia, Limnæa auricularis, L. peregra, and Planorbis carinatus. (Lyell, book iv. ch. xi.)
The upper Val d'Arno has yielded in its insulated freshwater deposits a few apparently lacustrine shells (anodon, paludina, neritina), and a vast number of mammalia: of which the following is a list (principally taken from Mr. Pentland's communication to Mr. Lyell):—
| Feræ | — | Ursus spelæus. |
| | — | —— cultridens. |
| | | Viverra valdarnensis. |
| | | Canis lupus? |
| | | Canis ——— |
| | | Hyæna radiata. |
| | | ——— fossilis. |
| | | Felis, new species. |
| Rodentia | — | Hystrix. |
| | | Castor. |
| Pachydermata | — | Elephas indicus (or E. primigenius?) |
| | | Mastodon angustidens. |
| | | ————— tapiroides. |
| | | Tapir. |
| | | Equus. |
| | | Sus scrofa. |
| | | Rhinoceros leptorhinus. |
| | | Hippopotamus major. |
| | | ——————— fossilis. |
| Ruminantia | — | Cervus euryceros? ​ |
| Feræ | — | Ursus spelæus. |
| | | Cervus valdarnensis. |
| | | ———— new species. |
| | | Bos urus. |
| | | —— taurus. |
| | | —— bubalo affinis. |
Cuvier also mentions the bones of a lophiodon from Val d'Arno. There is no geological evidence of the age of this deposit, except what its organic contents give. Mr. Lyell ranks it as meiocene: but, to judge from the list of mammalia, we should be disposed to place it in a later geological period; for here are no palæotheria nor anoplotheria of the Parisian eocene beds; no dinotheria or anthracotheria of the meiocene strata of Touraine, Käpfnach, &c.; while on the other hand, elephas indicus, hyæna radiata, and sus scrofa, if all living species! and Ursus spelæus, U. cultridens, Hyæna fossilis, Cervus euryceros, Bos urus, B. taurus,—all frequent in caverns and diluvial beds, &c., give to the list of animals a very modern aspect. By some authors (Meyer) the elephant of Val d'Arno is considered the same as that of the ordinary diluvium, and by Nesti it is called a new species (E. meridionalis).
The series of deposits in the upper Val d'Arno is as under:—
| Upper layer | — | Thick beds of yellow argillaceous sand. |
| Second | — | Thick masses of pebbles. |
| Third | — | Yellow sand, several fathoms thick, the middle and lower parts rich in bones. |
| Lowest bed | — | Thick blue argillaceous marl, with mica, with bones in the upper part. |
The pebbles are largest and most numerous towards the north; the coarse sand abounds in the middle, and the finer sediment in the southern part of the basin, -the sands and blue marls lie commonly horizontal. The bones lie in the middle of the valley, on the right side of the Arno.
The lower Val d'Arno contains only marine deposits. (Bertrand Geslin, Ann. des Sci. Nat.)
Agreeing in many respects with the freshwater aggregations in Val d'Arno, is a remarkable lacustrine deposit, of small extent (one fourth of a mile across), resting in a ​hollow of the new red sandstone formation, at Bielbecks, south of Market Weigh ton, in Yorkshire. The surface here is sandy and gravelly; for the sake of improving it the lacustrine marls below were excavated by the farmer, and in the lower part of the pit many bones and shells were found.
The excavation, being renewed under the direction of Mr. W. V. Harcourt, was continued to the bottom of the deposit, presenting in succession—
| 1. | Black sand at the surface. |
| 2. | Yellow sand, with a few pebbles of quartz and sandstone, to the depth of | 3 | feet. |
| 3. | Gravel, composed of chalk, pebbles, and sharp flints, to a depth of | 4½ |
| 4. | Grey marl, indented by the gravel No. 3, and containing rolled pebbles of quartz, limestone and sandstone of the carboniferous system, with chalk and flint, reaching the depth of | 10 |
| 5. | Black marl, with minute pebbles of chalk, and very few flints; at the bottom a few fragments of a fine-grained calcareous sandstone, such as belongs to the neighbouring red marl. Extreme depth | 22½ |
| 6. | Strong blue marl and some clay nodules. |
| | Flint gravel in marl. |
| | Strong blue marl. |
| | Flint gravel in marl. |
| 7. | Red marl, the basis of the whole deposit. |
No bones, shells, or vegetable remains were found in Nos. 1, 2, 3. 6. or 7. In the grey marl, No. 4., bones and tusks and teeth of the elephant, a bone of the rhinoceros, and a part of the horn of a deer were found, but no vegetable reliquiæ, and no shells. In the black marl, No. 5, most of the bones, and all the shells and vegetable reliquiæ occurred. The whole collection contained—
| Mammalia. | — | Elephas primigenius, | tusks, teeth, vertebræ, &c. |
| | | Rhinoceros tichorhinus, | teeth, tibia, rib. |
| | | Bos urus antiquus, | cranium, horns, teeth, bones of leg, &c. |
| | | Stag of great size, | parts of horn and metatarsal. ​ |
| | | Horse of large size, | metatarsal and phalangal bones. |
| | | Felis spelæa, | lower and upper jaw, and several leg bones. |
| | | Wolf, | humerus, radius, and ulna of right side, right lower jaw, condyle of the other. |
| Birds | — | Duck, | ulna, clavicle, tibia. |
| Insects | — | The green elytron of a species of chrysomela was recognised. | The green elytron of a species of chrysomela was recognised. |
| Mollusca | — | 13 species of land and freshwater shells, every one identical with species now living in the vicinity, were found mixed with bones of elephant, rhinoceros, viz.:— | 13 species of land and freshwater shells, every one identical with species now living in the vicinity, were found mixed with bones of elephant, rhinoceros, viz.:— |
| Helix nemoralis, caperata. | Planorbis complanatus, vortex, contortus, nitidus, spirorbis. |
| Pupa marginata. | Planorbis complanatus, vortex, contortus, nitidus, spirorbis. |
| Succinea amphibia. | Valvata cristata. |
| Limnæa limosa, palustris. | Tisidium amnicum. |
| (GeoL of Yorksh. vol. i. 2d edit.) ||
Mr. Morris, in his Memoir on the Deposits containing Mammalia in the Valley of the Thames (Magazine of Natural History, Oct. 1838), presents a variety of information bearing on the contemporaneous races of mammalia and mollusca. The mammalian remains are of the 'diluvial' æra (elephant, rhinoceros, hippopotamus, horse; ox; deer, Irish elk; vole, bear, lion, hyæna,—occurring at Brentford, Wickham, Ilford, Erith, Grays, Whitstable, Copford, Stutton, Harwich, Gravesend, Nine Elms, Lewisham, Kingslands. The shells found at Erith, Grays, Copford, Stutton and Ilford, are thus enumerated:—
Thus, the former co-existence of extinct mammalia, and numerous mollusca not in the smallest degree different from recent species living in the same climates, which was first ascertained near Market Weighton, and confirmed by Mr. H. Strickland's researches in Worcestershire, is abundantly established by a large induction of instances.
Mr. Charlesworth, whose researches on the supracretaceous deposits of the eastern counties have led to other valuable results, presents, in the following general view of the beds which there occur above the chalk, a simple classification of the mammaliferous strata. (Reports of the British Association, for 1836, p. 85.)
| Section I. | Beds containing numerous remains of terrestrial mammalia:— |
| | 1. Superficial gravel, containing bones of land animals, probably washed out of stratified deposits. |
| | 2. Superficial marine deposits of clay, sand, &c., in which the shells, very few in number (10 or 15 species), may all be identified with such as are now existing. (Brick earth of the river Nar, Norfolk.) |
| | 3. Fluviatile and lacustrine deposits, containing a considerable number of land and freshwater shells, with a small proportion of extinct shells; (mammalian remains in great abundance. (Ilford, Copford, and Grays, in Essex, Stutton in Suffolk.) ​ |
| | shells, with a small proportion of extinct shells; (mammalian remains in great abundance. (Ilford, Copford, and Grays, in Essex, Stutton in Suffolk.) |
| | 4. Mammaliferous crag of Norfolk and Suffolk, hitherto confounded with "red crag," containing about 80 species of shells; proportion of extinct species undecided. (Bramerton, near Norwich; Southwold and Thorpe in Suffolk.) |
| SECTION II. | Beds in which few traces of terrestrial mammalia have yet been discovered:— |
| | 5. Red crag. (It contains mastodon, &c.) |
| | 6. Coralline crag. |
| | 7. London clay. (It contains quadrumana, &c.) |
| | 8. Plastic clay. |
Modern Lacustrine Deposits.
Some small lakes are situated at this day, and many were in former times, so as to receive no considerable river, but many small runlets from the adjacent slopes. Under ordinary circumstances, the running streams throw into lakes only carbonate of lime, and other dissolved or suspended matters, which may be diffused with great equality in the water, and at length settle on the bottom in one or more layers. In times of abundant rain, coarser sediments are carried into such lakes from more numerous points of the margin, and thus the whole lake is filled toward the edges by narrow concentric sloping layers of sand and gravel (s), which are intermixed with layers of finer clay or marly substance (c), as in the diagram No. 80.; which also shows,
above several deposits of coarse and fine earthy ​materials, a single bed of peat (p), composed of the disintegrated portions of plants swept down from the land, or produced by vegetable growth on the spot. Above such a peat-layer it is usual to find in the middle parts of old lakes very fine marls, with or without shells, wholly unmixed with coarser sediments. This circumstance is commonly observed in many of the ancient lakes of Holderness, where, usually, the middle part of the lake-bed contains little or no coarse sand or gravel.
In these fine marls tubular passages, left by the roots of aquatic plants, frequently appear; and shells of freshwater (or land) species commonly occur. Heads and horns, and sometimes entire skeletons of the red deer, the Irish elk, beaver, &c., are buried in the marls or peat, under circumstances which indicate in some cases the drifting of their dead bodies by water, and in others require the supposition that the animals had entered the lake through choice or fear, and been drowned and covered by sediments.
Certain fine layers, in freshwater lakes of Denmark, have been found by Dr. Forchhammer to be composed of the siliceous matter arising from the disintegration of the epidermis of some fresh water plants. Seeds of Chara occur in others; and it is probable that the calcareous substance of this plant has contributed not a little to the mass of friable marls which lie in many lakes.
On the coasts of Yorkshire and Lincolnshire, lacustrine deposits occur at many points, and present a considerable variety of circumstances as to level above or below the sea, sandy, marly, or peaty composition; but are always governed by the general condition, that they occupy small hollows on the surface of the diluvial accumulations. "All the lacustrine deposits containing peat, which I have inspected in Holderness, agree in this general fact, that the peat does not rest immediately upon the diluvial formation beneath, but is separated from it by at least one layer of sediment, which is ​seldom without shells. The peat is very generally confined to a single layer, and shells are seldom found above it. Supposing that all the varieties which I have witnessed in different places existed together, the section would be nearly in the following general terms:—
Of these the most constant beds appear to be Nos. 1, 2. and 5.; and in general these constitute the whole deposit. The peat varies from 5 feet in thickness to less than so many inches. In a few instances, the lower clay, No. 5, contains no shells: the species which so occur are not always the same: Cyclades and small Paludinæ are the most plentiful: Anodons occur at Skipsea and Owthorn, but I did not find them elsewhere. Skeletons, and detached horns of the Irish elk (Cervus euryceros), red deer, and fallow deer, occur in it at several points." (Geol. of Yorkshire, vol. i.)
A deposit of similar origin in Berwickshire, full of limnæana and planorbes, envelops horns of the red deer and bones of the beaver. At Silverdale, near Burton in Kendal, and at other points round the bay of Morecambe, deposits from fresh water, probably of equal antiquity, occur at such levels that the tide might easily flow over them. They are usually covered by peat at the surface, and composed of shell marls in considerable quantity, the shells belonging to Limnæa, Planorbis, Cyclas, Pisidium, &c., and apparently identical with existing species. Occasionally the bones of the great Irish elk occur in these marls (a fine pair is ​to be seen over a doorway in Garstang); and from them Lee states the head of hippopotamus, figured in the Natural History of Lancashire, to have been derived.
To this period we may also refer the lacustrine and peat deposits of the Isle of Man, and Ireland, which have yielded the fine skeletons of the Irish elk, now standing in the museums of Edinburgh and Dublin. The specimen in the Royal Dublin Society's collection was obtained by archdeacon Maunsell, at Rathcannon, near Limerick, in shelly marl, 1½ to 2½ feet thick under peat 1 foot thick, and above blue clay 12 feet thick or more. According to Mr. Griffith, it is in these white shelly marls, under peat, that all the skeletons of the Irish elk have been found, which agrees with what has been observed in England. (Outline of the Geology of Ireland, 1838.)
"At Milk Pond in New Jersey, countless myriads of bleached shells of the families limnæana and peristomiana, analogous to species now living in the adjoining waters, line and form the shores of the whole circumference of the lake to the length and depth of many fathoms. Thousands of tons of these small species, in a state of perfect whiteness, might be used for agricultural purposes. In one case, a perforation was made 10 or 12 feet deep, and did not pass through the mass. It forms the whole basin of the lake, and may at some future time become a tufaceous lacustrine deposit." (Lea, Contrib. to Geol. p. 225.)
Mr. Lyell's description of the deposits which are still proceeding in Bakie Loch, Forfarshire, offers an excellent type of comparison for analogous deposits of older date. The sediments in this lake are principally two beds of calcareous shelly marls, separated by a loose sandy deposit, covered by a layer of peat with trees, and resting on fine sand and detritus. The calcareous matter is supplied by springs, and in general is of a soft friable nature; but near the springs it is solidified, and receives the title of "rock marl" It is principally to the vital functions of limnæa, cyclades, and charæ, ​that the separation of the calcareous matter from the water of the lake is owing; and though, in some parts of the deposit, all trace of their individual forms is lost, (as in certain coral reefs the organic structure is obliterated by the decomposition and re condensation of the mass), there is reason to think the greater part of the marls is really a congeries of organic exuviæ. Horns of the stag lie in the marls. There are no unionidæ among the shells.
Subterranean and Submarine Forests.
Buried Trees on the Course of a River.
It appears that sometimes the violence of river floods was so great as to sweep down to the tide-line abundance of land plants, which, covered by sediment, constitute by their accumulation one kind of buried or subterranean forest. A very interesting case of this kind was exhibited some years ago, by the deep cutting of a canal connected with the Aire and Calder navigation, near Ferrybridge. At a depth of 1 2 feet from the surface of the fine alluvial sediment, here occupying the broad valley of the Aire, a quantity of hazel-bushes, roots, and nuts, with some mosses, freshwater shells (Limnæa, Planorbis, &c.), and bones of the stag were met with. In some part of the superjacent sediments, an English coin was found, and oars of a boat were dug up. Where a little water entered this peaty and shelly deposit, from the adjacent upper magnesian limestone, it produced in the wood a singular petrification; for the external bark and wood were unchanged, but the internal parts of the wood were converted to carbonate of lime, in which the vegetable structure was perfectly preserved. In like manner, some of the nuts were altered; the shell and the membranes lining it were unchanged; but the kernel was converted to carbonate of lime, not crystallised, but retaining the peculiar texture of the recent fruit. ​
What renders this curious case of elective molecular attraction the more decisive, is the fact that, in the same deposit, sulphuret of iron was found, but only on the outside of wood; and, from the whole we learn that, just as in the chambers of ancient ammonites, and cells of the bones of saurians, the carbonate of lime has passed through shell, membrane, and bone, and penetrated precisely to those spots where it might seem most difficult for it to arrive, so, in the comparatively modern nuts and woods, the same substance has been similarly transferred to the interior parts, through solid matter; while sulphuret of iron in both cases remains on the outside.
In this particular case, no reasonable doubt can exist (we conceive) that the peaty deposit, full of land mosses, hazel-bushes, and freshwater shells, was water-moved, and covered up by fine sediments from the river and the tide. In some of the old lakes of Holderness, the same mechanical explanation appears applicable: an example has been furnished (Waghen in Holderness), which shows on the same spot, first, the accumulation of violently agitated water ("diluvium"); then a deposit of fine clay, and several layers of peat and trees of different kinds; and over all, the stumps of pines (Scotch fir), which seem to be in their place and attitude of growth.
On Chat Moss, near Manchester, and in other situations, the stumps of oak trees appear in the attitude of growth, though the proof of the trees having grown there is seldom completed by the actual tracing of the roots laterally, or, what is still more important, downwards in the clay. Dr. W. Smith has observed, in the deposits of trees in East Norfolk, differences according to the soil; birches and alders on sand, and oak trees on an argillaceous bed.
In England, Wales, and Scotland, deposits of this nature, full of trees and vegetable reliquiæ of different kinds, abound much more on the sea coast, and in alluvial land which has been deposited within the ancient sea boundary, than elsewhere. Occasionally, it is true, ​amidst the mountains of Westmoreland (as in a small hollow between Kirkby Lonsdale and Kendal) and Scotland (as at the head of Glencoe), trees, rooted or prostrate, occur mixed with peat; but it is on the shores, or in the midst of the alluvial plains of Yorkshire, Lincolnshire, Cambridgeshire, West and East Norfolk, Cornwall, Somersetshire, Swansea, Cheshire, Lancashire, the mouths of the Clyde, Forth, and Tay, the shores of the Orkneys and Hebrides, that the most abundant of these buried forests occur. This general fact justifies the title of Submarine Forests, commonly applied to them, and is of great importance in reasoning on the circumstances of their accumulation. On the contrary, the greater part of the Irish bogs are inland accumulations; but they occupy the lower plains of the country, and are often margined by gravel banks, and abound on the line of the Shannon, which is a stream of very little declivity.
The trees contained in these deposits are identical with those now growing in the vicinity, hazel branches and nuts being very common; with them are occasionally found fluviatile or lacustrine shells, and bones of deer and other land animals; but, as far as we know, no marine mollusca, and seldom marine remains of any kind. The level of the buried trees is seldom above, but generally below, the high-water line, and often level with, or not infrequently many feet, or even yards, below, low-water. On the sides of the Humber, below Hull, submarine peat and trees are found at various depths below low water; at the mouth of the Tay, level with it; at Swansea and Owthorne, sloping beneath it; at Sutton, near Alford, on the Lincolnshire coast, visible only at the lowest ebb-tides.
As De Luc suggests, with regard to the layers of peat resting on clay at Rotterdam (Hist. de la Terre et de l'Homme, tom. v. p. 325.), we may believe the deep buried trees and peat of the sides of the Humber to have been drifted; but this is not the explanation generally proposed by observers, who appear almost without exception ​impressed with the belief that the trees grew on the spots where now they lie prostrate, and often buried beneath lacustrine or fluviatile (seldom marine) sediments.
To account for their occurrence, at levels and under circumstances which now render the growth of trees almost impossible, it is sometimes supposed that the waste of the coast has opened to the sea some secluded valley of peat, which, originally full of moisture, like a sponge, was raised thereby above the tide-level, but, on the loss of its seaward barrier, was drained, and sunk considerably. (Dr. Fleming, in the Quarterly Journal of Science, 1830.) But in most cases a real subsidence of the land is appealed to. (Dr. J. Correa de Serra, in Phil. Trans. 1799.)
The evidence in favour of the opinion that the trees really grew on the spots where now they appear has generally been thought satisfactory by geological writers; it is, however, not always so exact and complete as might be desired, because the circumstances which accompany the submarine forests have seldom been carefully inquired into with this object in view. Speaking of the deposits on the shores of the Frith of Tay, Dr Fleming observes, that "the upper portion of the clay, on which the vegetable accumulation immediately rests, is penetrated by numerous roots, which are changed into peat and sometimes into iron pyrites" Stumps of trees, with roots attached, are observed on the surface of the peat. Leaves, stems, and roots of equisetacese, graminea?, and cyperaceae, with roots, leaves, and branches of birch, hazel, and probably alder, constitute the mass of the deposit. Hazel nuts without kernel abound. All these remains are much flattened where they lie horizontally, but the stems which remain erect retain their cylindrical figure. This is exactly similar to the condition of stems of trees in a coal district.
One of the most interesting deposits of peaty matter is that associated with drifted tin ore, on the coast of Cornwall. The deposit of Sandycock, between the parishes ​of St. Austle and St. Blazy, is described by Mr. P. Rashleigh (Geol. Trans. of Cornwall, vol. ii. p. 281.) as occupying a vale, which has received drifts from the sea, as well as from the country above. The series of beds is thus noticed:—
| | | ft. | in. |
| 1. | Vegetable mould, about | 0 | 3 |
| 2. | Gravel and micaceous sand, mixed with fine loam, in alternate beds of various depths, making together | 8 | 3 |
| 3. | Light-coloured clay, with a little mica, and a few roots of vegetables nearly decayed | 5 | 3 |
| 4. | Black peat | 4 | 1 |
| 5. | Light coloured clay | 1 | 4 |
| 6. | Stiff clay of a light brown colour, with some decayed roots of vegetables. The clay was spotted with light blue (phosphate of iron) | 3 | 10 |
| 7. | Sea sand and clay mixed | 3 | 0 |
| 8. | Very fine sea sand, together with mica and small fragments of shells and killas | 4 | 0 |
| 9. | Coarser sand without shells | 6 | 0 |
| 10. | A solid black fen, with a few remains of vegetables, in which are round globules of the size of middling shot, but not harder than the fen. This substance is not made use of as fuel | 2 | 10 |
| 11. | Tin ground, and loose stones of all sorts. This bed varies in thickness from 1 ft. to | 6 | 0 |
| 12. | Kilias, the general base of the deposit. |
At Mount's Bay (Dr. Boase, in Trans. Geol. Soc. Cornwall), the vegetable deposit is covered, on the sea coast, by a thick bed of shingles, and inland, appears beneath a marsh. Elytra of insects appear in this deposit, very little changed from their pristine beauty.
De Luc paid great attention to peat deposits and buried forests in all situations. In his observations on Holland he makes frequent mention of the low level of the peat and silt deposits, attributing this circumstance to a subsidence of those materials in the course of their desiccation. From M. Van Swinden he learned that there were lakes in Friesland, which had once been woods. "Le Fljuessen Meer, par exemple, grand lac ​au N. E. de Staveren, étoit encore un bois en 489; et ce lac, ne pourroit etre désséché aujourd'hui que par artifice." The soil of Holland, which has been longer enclosed in banks than Friesland, is on a lower level. The same explanation applies to the fact, well known near Lynn, that the land which has been regained since the Roman sea banks were made is on a higher level, and of greater value, than that which was enclosed by the Romans; and outside of "Marshland," as this tract is called, the new foreshores are sometimes still higher.
For the following interesting fact we are also indebted to De Luc:—
"Près de la Scanie, dans la mer Baltique, est une isle nommée Bornholm, environ née de collines de sable, dont le milieu est une vaste Tourbière, sous laquelle on trouve quantite de sapins, couches de la circonférence au centre. Cette derniere circonstance, pour le dire en passant, prouve toujours mieux que ces arbres n'ont pas été abattus par des inundations, mais par les vents. Ici, plongeant du haut des collines, et tout le tour en differens terns, les vents out renverse ces arbres quand la tourbe a été profonde et molle, et les ont ainsi couchés de la circonférence vers le centre." (Hist. de la Terre, Partie X. Lettre cxxvi. tom. v. p. 222.)
He applies this fact to explain the origin of coal from peat, and enters into a short explanation of the mode by which he conceives the submerged peat was covered by the argillaceous schistus of its roof, enveloping the plants then growing on the peat; remarking that both elevations and depressions of land happened before the final desiccation of our continents, and noticing the differences of the ancient and living flora of the peat moors.
Turf Moors.
Submarine and subterranean forests are almost universally associated with peat, or turf, as it is called in the north of England, and indeed, generally, they constitute ​a considerable portion of the vegetable mass. There are, however, peat bogs in which no timber lies buried; and many of these are daily and hourly augmenting their area, and increasing their depth, by the growth of living, and the accumulation of dead, plants. Though the gigantic "peat plant," as described by some writers, is an imaginary creation, sphagnum palustre and other humble mosses appear to deserve the epithet, and heather is a very common accompaniment. To an antiseptic property, imparted by this latter plant, De Luc was disposed to ascribe the conservation and accumulation of the various vegetable substances which occur in peat.
There are few shallow lakes in the interior of England, and especially in the sandy tracts, like Cheshire and Nottinghamshire, which are not, in some part or other, encroached on by the growth of peat. Preceded by reeds, this substance slowly advances over the sandy or pebbly bed, and changes to damp and shaking meadows the surface of the upper end of the lake. The upper end of Derwentwater, Ulswater, and many of the mountain lakes in Wales, display this growth of peat completely; and in many of the wide bogs of Ireland, the Isle of Man, and Arran, we see the process finished, and the lakes wholly obliterated in a spongy carbonaceous mass. In a similar way, many of the valleys without lakes, and many of the elevated slopes and summits of hills, especially on gritstone or granite surfaces, both in the south of England (Dartmoor), among the Yorkshire hills (Watercrag, Great Whernside), and the Cumbrian mountains (between Skiddaw and Saddleback), are covered with great depths of peat, in which trees are never seen. Similar facts appear among the Grampians, on the mountains near Enniskillen, and in other parts of Ireland; and these extensive tracts of "moor," as De Luc calls the peat deposits in the north of Germany, are supposed to be no where so abundant as in northern latitudes.
The bogs of Ireland lie principally in the central parts, on the wide plains of mountain limestone, and ​are supposed to cover one-tenth of the surface of the island. The thickness of the peat varies from 12 to above 40 feet; the upper layers being very fibrous, and showing clearly the structure of the component plants; the lowest, a close dense mass, much resembling coal, and breaking with conchoidal fracture.
Most of the Irish peat bogs contain trees, which in some cases lie at the bottom; and it may be thought that the whole deposit is little else than the accumulated ruins of a long succession of forests; in other cases the vegetable mass, whether thus accumulated or aggregated by drifting, has served as the basis of a new race of trees, whose roots remain at the surface. And it is observed, in the "Reports" on the bogs of Ireland, that in that country it is common to find trees, in the place and attitude of growth, rooted on peat seven feet thick. This is especially the case with fir trees (so at Waghen, in Yorkshire), but oaks are commonly found to rest on the gravelly basis of the bog. Shelly marls frequently lie under the peat, and indicate that, in such cases, the origin of the bog is to be ascribed to the same process which is constantly going on to extinguish some modern lakes. This is the view adopted by the ordnance surveyors, in their Report on the County of Londonderry.
Antiquity of Subterranean Forests.
Closely connected with the determination of the question whether the trees of the "submarine forests" grew where now they lie enveloped in peat, are facts ascertained regarding the antiquity of certain of these deposits. De Luc, who looked on phenomena of this nature with great interest, on account of their important bearing on two capital points to which his mind was continually turning, viz. the origin of coal, and the antiquity of our continents,—notices, a few leagues from Winsen (near Hamburg), the occurrence of four or five inches of vegetable earth (terre végétable) above ​ancient burial mounds, composed of heaps of stones, and in closing frequently an urn of burnt bones. Observations nearly similar may be easily made on the heathy and peaty moors of the elevated parts of the north of England, where tumuli and ancient roads and causeways are nearly concealed by the growth of vegetables and aggregation of sands.
But the accumulation of peat from living plants is in some places so rapid, that it seems endowed with an inexhaustible vitality, and may be cut like a copsewood every fourteen years. And in countries like Hatfield Chace, which are one wide turf moor, the occurrence of Roman coins, and axes yet fixed in the wood, appear to prove at once the fact that the trees grew on the spot, and fix the historic date of their destruction.
De Luc mentions the discovery of a medal of Gordian 30 feet deep in peat at Groningen. Besides other proofs of the modern origin of this substance, near Bremervörde, a small hill of "hard land" or "geest," is stated to be overgrown with peat, and its title "Isleberg" shows the modern date of this overgrowth. (Lettres sur l'Histoire de la Terre et de l'Homme, tom. v. p. 264.)
'De Luc ascertained that the very site of the aboriginal forests of Hercinia, Semana, Ardennes, and several others, are now occupied by mosses and fens; and a great part of these changes has, with much probability, been attributed to the strict orders given by Severus and other emperors to destroy all the wood in the conquered provinces." (Lyell, Princip. book iii. ch. xiii.)
One of the most valuable of all the descriptions of subterranean forests is that of Hatfield Chace in Yorkshire, by the Rev. A. De la Pryme (1701). Of 180,000 acres here, constituting the largest chace of red deer in England which belonged to Charles II., about half was yearly drowned by vast quantities of water. Sir Cornelius Vermuiden drained it, at a cost of 400,000l., cutting amongst other great works a new channel for the tide river Don, which is now called ​Dutch River, one of the old channels, which entered the Aire, being now nearly filled up. In the beds of the rivers, below the marshland, and all round to the highlands of Lincolnshire and Yorkshire, are found "vast multitudes of the roots and trunks of trees of all sizes, great and small, and of most of the sorts that this island either formerly did, or that at present it does, produce; as firs, oaks, birch, beech, yew, thorn, willow, ash, &c.; the roots of all or most of which stand in the soil in their natural position as thick as ever they could grow, as the trunks of most of them lie by their proper roots. Most of the large trees lie along about a yard from their roots (to which they evidently belonged, both by their situation and the sameness of the wood), with their tops commonly north-east; though, indeed, the smaller trees lie almost every way across the former, some over and others under them." A third part of the trees were of the fir tribe (some 30 yards long and more), and in such condition as to be sold for masts and keels for ships; oak, black as ebony, abounded, 35 yards and more long, and useful in carpentry; ash trees were the only ones found decayed. "Some of the fir trees, after they were fallen, have shot up large branches from their sides, which have grown up to the height and bulk of considerable trees." (Hutton's Abridgment, Phil. Trans. vol. xxii.)
Many of the trees, and especially the fir trees, have been burnt, sometimes quite through; others chopped, squared, bored through, or split, with large wooden wedges and stones in them, and broken axe-heads, somewhat like sacrificing axes in shape, and this at depths, and under circumstances, which exclude all supposition of their being touched since the destruction of the forest. "Near a large root in the parish of Hatfield were found eight or nine coins of some of the Roman emperors, but exceedingly defaced with time; and it is very observable, that, on the confines of this low country, between Burningham and Brumley in Lincolnshire, are several great hills of loose sand, under which, as they are yearly ​worn and blown away, are discovered many roots of large firs, with the marks of the axe as fresh upon them as if they had been cut down only a few weeks." (Hutton's Abridgment, vol. xxii.)
Hazle nuts, and acorns, and fir cones, in great abundance, lie heaped together at the bottom of the soil; and "at the bottom of a new river or drain (almost 100 yards wide and 4 or 5 miles long), were found old trees squared and cut, rails, stoops (gateposts), bars, old links of chains, horse-heads, an old axe somewhat like a battle-axe, and two or three coins of Vespasian. But what is more remarkable, is that the very ground at the bottom of the river was found in some places to lie in ridges and furrows, thereby showing that it had been ploughed and tilled in former days." (Ibid.)
Mr. De la Pryme was informed by Mr. E. Canby, that he had found an oak tree which was 4 yards across at the base, 3½ yards in the middle, and 2 yards across the top; and the length of this fragment (the top was gone) was 40 yards. The same person found a fir tree 36 yards long, and estimated it to be deficient 15 yards = 51 yards or 153 feet. (The highest fir tree which has fallen under our observation in England, is a spruce fir near Fountain's Abbey, stated to be 1 1 8 feet above the grass.)
The roots of the fir trees have been observed to be in the sand, and those of the oak trees in clay.
"About 50 years ago," says Mr. De la Pryme, "at the very bottom of a turf pit, there was found a man, lying at his length, with his head upon his arm, as in a common posture of sleep, whose skin being tanned, as it were, by the moor water, preserved his shape entire; but within, his flesh and most of his bones were consumed."
Another case of this nature was brought under the examination of the author of this volume, by Mr. W. Casson, of Thorn, who forwarded to the Yorkshire Museum (1831), the head of a fallow deer, found in the peat near that place, in a singular condition. The bones and teeth were, in fact, changed to leather; the ​hardening earth having been dissolved in the sulphuric acid, which is of ordinary occurrence in the peat of Yorkshire, and the residuary gelatine changed to leather by the tannin.
The prostration of the trees towards the north-east has been noticed by Verstegan and De Luc, in the morasses of the Netherlands and Germany. De Luc, speaking of the abundance of trees lying below the peat of the country near Bremervorde, attributes their direction from S.W. to N.E. to the prevalent winds and rains from the S.W.; he also notices the chopping and burning of the trees. (Lettres, torn, v.)
The conclusion of Mr. De la Pryme, "that the Romans were the destroyers of all the great woods and forests which we now find underground in the bottom of moors and bogs," has been generally adopted by geologists; and, with regard to districts where the Roman sway was impotent or unknown, as Wales, the Isle of Man, and Ireland, the destruction of many forests is charged on later conquerors.
If, from the contemplation of evidence concerning the historic date of subterranean forests furnished by the coins of Rome, and ruder works of earlier people, we turn to the monuments of nature, the remains of men and quadrupeds, which occasionally present themselves in drains and other excavations, we find the impression, that the overthrow of the forests took place in comparatively modern geological times, materially strengthened. For, while the bodies of men and women, which have been found in Solway Moss, in the bogs of Ireland, and other parts, agree with the evidence of coins, axes, and canoes, the bones of quadrupeds belong, almost in every instance, to existing species, as the red and fallow deer, wolf, beaver, horse, ox, and sheep; the insects and mollusca, and all the trees and plants, are of types yet living in the same vicinity.
Yet, to this general rule are, at least, two seeming exceptions. The head of a hippopotamus is figured by Lee, in his History of Lancashire, and noticed as found ​under the peat of Lancashire; works of human art being also mentioned; and bones and antlers of the great extinct elk of Ireland occur in many of the peaty and marly Deposits of Ireland, the Isle of Man, Lancashire, and Yorkshire.
Another example of peat deposits connected with shell marls, which contain quadrupeds of the same races as those usually supposed to characterise the diluvial deposits, occurs at Wittgendorf, near Sprottau (Silesia). Here, according to Meyer (Palæologica), below a thin bed of drifted sand and pebbles, in the lower parts of a peat deposit, 6 to 8 feet thick, and, also in marls below, lie bones of Elephas primigenius, oxen, deer, and fish, with cyclostomæ. In these cases, the bones and shells show no sign of abrasion.
If we turn to America, and take as an example the circumstances which accompany the bones of the great mastodon, the inference previously adopted as to the age of the peat deposits is confirmed; for these certainly date from an epoch subsequent to the dispersion of diluvial detritus. But, as regards the animal remains, we learn that a tooth of the mastodon occurred at Fort M'Henry, near Baltimore, below "diluvium;" and it is well known that, at Big Bone Lick and in New Jersey, and elsewhere, nearly complete skeletons of Mastodon giganteus occur in peat and shelly marls of comparatively recent date, along with extinct and living species of oxen and deer.
"From all the facts before me," observes Professor Rogers, in his Report to the British Association, 1834, on the geology of North America, "I have little hesitation in giving my opinion, that the extinct gigantic animals of this continent, the mastodon, elephant, megalonyx, megatherium, fossil bos, and fossil cervus, lived down to a comparatively recent period, and that some of them were in existence so long ago as the era anterior to that which covered the greater part of this continent with diluvium."
The conclusion here presented may very probably, or ​rather certainly, be extended to the Irish elk, of which the perfect specimens appear to be of comparatively modern date; but various fragments, apparently of the same species, have been detected in the ossiferous caves and gravel of northern regions, which contain the mammoth and rhinoceros. It will depend upon farther research, whether this conclusion may be extended to the extinct elephant, hippopotamus, and rhinoceros, and to the living stag, ox, horse, and wolf. Concerning these latter animals, we can only affirm, that it has been found impossible to distinguish, by any constant marks, the specimens found in ancient caverns and gravel beds, from those now living in the same regions.
* ↑ Saussure, Voyages dans le Alpes; Agassiz, Etudes sur les Glaciers; Forbes, Travels in the Alps, and Phil. Trans; Mallet, Proc. of Dublin Geol. Soc.; Hopkins, Phil. Magazine, Camb. Phil. Trans., may be specially cited in regard to glacial movement. De la Beche has collected a body of information in his Geological Observer.
* ↑ The glacier of the Aar was found by Agassiz to fill a valley 780 feet deep.
* ↑ Hopkins in Proceedings of Geol. Soc. 1852.
* ↑ Forbes's Travels in the Alps.
* ↑ Camb. Phil. Trans.
* ↑ Weight diminished to ⅓.
* ↑ The true relations of the Stonesfield fossil jaws referred by M. Cuvier, Mr. Owen, and M. Agassiz to marsupialia, may now be regarded as settled.
* ↑ Mantell has described a large Unio from these beds.
* ↑ Brit. Association Reports, 1850.
* ↑ See Brodie's Fossil Insects.
* ↑ Mr. Morris remarks that the shells which occur at these localities are of land and freshwater kinds, not marine, and agrees with the opinions of Mr. Charlesworth. that mammalian remains are more commonly associated with fluviatile and lacustrine, than marine and detrital deposits, a conclusion which is acquiring fresh importance every day. We have, in fact, preglacial and post glacial elephantine remains.