CHAPTER XII.

ALLUVIUM. -RECENT FORMATIONS.

THE term diluvium, applied to the great collections of gravel and detached blocks, from the idea that they originated with the historic deluge, is still retained in such a connection, because those accumulations indicate the extraordinary action of water, either in the form of strong oceanic currents, while the localities were in a state of submergence, or of waves of translation overspreading the land, produced by submarine disturbance, or torrents proceeding from rapidly-melting glaciers. On the other hand, the term alluvium is used to denote those formations of the modern and current epoch which result from the ordinary action of water; and, etymologically, it can only be properly employed in relation to aqueous products. But its more comprehensive application is sanctioned by usage,

Cyclopean Remains, Mycene.

and may be granted in this place as a matter of convenience. It occurs therefore at the head of this chapter as a general title for those superficial formations which appear to have transpired since our planet received its present configuration of land and sea, and Man became its occupant and master, which are now in course of production, whether due to aqueous, igneous, atmospheric, organic, or human agency, the effects of one or of several of these causes combined. In some of these recent aggregations we meet with the remains of man and contemporaneous animals and plants, with human utensils and ornaments also, characteristic of the ancient British age in our own country, the Etruscan in Italy, the Pelasgic in Greece, and the era of the Pharaohs along the banks of the Nile. But we discover no bones that can be specifically identified as those of the great quadrupeds of the drift, which probably mostly perished in those physical changes under which it accumulated, subsequent to which the present state of things commenced, and man, with the existing animal races, was created. Some have supposed, indeed, that America had its droves of mastodons and megatherida browsing upon its savannahs down to a comparatively modern period; and good evidence supports the idea, that the gigantic horned elk continued to be an inhabitant of Europe coexistent with the human race. Such conclusions, supposing them to be established, are in harmony with the views already expressed respecting the first appearance of the present animal races as produced around several centres of creation, not contemporaneously, our sacred history dealing merely with one of those districts, the most recent, that in which the primitive man was placed. There is no difficulty in conceiving of the extinction of some tribes of animals as the consequence of current events; such as one of those unusually long droughts to which South America is occasionally subject, when, as during the gran seco, which lasted three successive years, it was calculated that from a million and a half to two millions of animals died exhausted by hunger, the borders of all the lakes and streamlets in the province of Buenos Ayres being long afterwards white with their bones. The case of the dodo, a large and remarkable bird existing in the Mauritius during the early voyages to the East, appears to be a well-authenticated instance of the death of a species in comparatively recent times; and now of several races dangerous to man, or useful to him for their skins, it may be predicated that the period of their extinction is not very distant.

Of formations contemporaneous with the present era, an arrangement may be adopted which classifies them according to the agency immediately operating in their production. 1. Organic-coral reefs; peat-mosses or bogs; subterranean forests.

Formations of coral-the agglutinated skeletons of departed races of coral zoophytes, composed of carbonate of lime secreted from the ocean, with broken shells, echinites, and sand, all cemented together into hard calcareous rock-are among the most interesting organic constructions of modern as of ancient times, now in course of augmentation from the living swarms. Detail here will be unnecessary, having previously referred at large to the islands which owe their origin to these marvellous creatures; and also to the submerged reefs advancing surely towards the surface of the waters, though at an excessively slow rate to us, which a slight submarine eruption might elevate into chains and clusters of islets, the agency undoubtedly which has uplifted some of the coralline formations of the Pacific thousands of feet above the deep. The island of Tahiti, composed almost entirely of volcanic rocks, has on the summit of its highest mountain a coralline stratum; a similar bed occurs in the Isle of France, between two lava currents; and all voyagers of modern date-Beechey, Quoy and Gaimard, Stutchberry, and Darwin-concur in the opinion that the coral reefs and islands proceeding in the Pacific do not go down many hundred feet below the surface of the waves, but rest upon submarine volcanic ridges and rocks. The cut in the next page represents species of three common genera of corals: Caryophyllia, the external character of the polyparium or stony skeleton of

a group of the zoophytes, being cylindrical, either simple or branched; Madrepora, character arborescent or frondescent; and Meandrina, character either turbinated or globular, the surface more or less confluent, but marked with sinuous ridges and valleys. We have had occasion repeatedly to notice corals in the more ancient strata of the globe, especially in the Silurian rocks, evidencing the existence, in far remote ages, of kindred forms of vitality to those that now inhabit the ocean; but their geographical range was then more extended than at present. Now it is tropical; but then it reached to high latitudes, intimating the higher temperature of the northern seas, and the general prevalence of a warm climate, in the earlier stages of our planet's history.

Peat-mosses or bogs are organic products, consisting of vegetable matter spread over extensive areas in northern latitudes; for in tropical climates, except on high lands, the decomposition of vegetable substances proceeds so rapidly, that they are resolved into their ultimate elements before peat can be produced, or they are removed by insects. Accordingly, formations of this kind are limited chiefly to the colder regions of the globe. They are usually found in level situations, or on declivities abounding with springs, where varieties of plants are nourished, the decay of which produces a spongy vegetable mould, to which fresh contributions are annually made from the annual decay of new races. A morass, yielding and quivering to the tread, is the first product. This often becomes a firm deposit, as the accumulation increases, or when, from accidental causes, the mass is drained, or the supply of water ceases; but frequently the upper part is hard, yet trembling, arising from the slight consistency of the substratum. These are called moving-bogs in Ireland, and quaking-mosses in Scotland, and are frequently perilous to travellers and cattle. Gilpin describes the Solway moss- a flat area, about seven miles in circumference, on the confines of England and Scotland-as covered with grass and rushes, presenting a dry crust and fair appearance, but shaking under the least pressure, the bottom being unsound and semi-fluid. He states that the adventurous passenger, who sometimes in dry seasons passes this perilous waste to save a few miles, picks his cautious way over the rushy tussocks as they appear before him, for here the soil is firmest; but if his foot slip, or if he venture to desert this mark of security, it is possible he may never more be heard of. "At the battle of Solway, in the time of Henry VIII. (1542), when the Scotch army, commanded by Oliver Sinclair, was routed, an unfortunate troop of horse, driven by their fears, plunged into this morass, which instantly closed upon them. The tale was traditional, but it is now authenticated, a man and horse in complete armour having been found by peat-diggers in the place where it was always supposed the affair had happened. The skeleton of each was well preserved, and the different parts of the armour easily distinguished."

The composition of peat, according to Sir H. Davy's analysis, consists of from sixty to ninety-nine parts of vegetable matter in the hundred, with a residuum of earths analogous to the subjacent strata, and oxide of iron. Three specimens obtained from different parts of the United States, upon analysis, yielded

Lichens, moss, reeds, grasses, heaths, and shrubs of several kinds may commonly be traced in peat; but one particular species of moss, the Sphagnum palustre, enters into it most abundantly, the upper portion of which continues to flourish vigorously, while the lower portion decays and forms a soil. This contemporaneous vegetation and decay, proceeding for a series of years under favourable circumstances, rapidly forms a thick and extensive accumulation, embedding the trees that may have been growing in the locality, previously prostrated by the winds through the roots rotting. George, earl of Cromartie, relates a remarkable case of the rapid formation of a peat district, in about half a century, between the years 1651 and 1699, near Loch Broaw, on the west of Ross-shire. In 1651, when nineteen years of age, he noticed the spot as a plain covered with standing wood, the trees being entirely leafless and stripped of their bark, evidently a pine forest in one of its last stages. Some years afterwards, when again in the neighbourhood, he found the plain completely denuded of its trees, and presenting the aspect of a flat green ground spread over with moss. Upon inquiring what had become of the trees, and who had carried them away, he was informed that they had been all uprooted by the winds, and lay underneath the green moss; and before the year 1699, he states that the country people came there to dig turf and peat. It appears that the fallen timber, upon being soaked by the rains, first became coated with several species of fungi. An adhesive matter formed by the decay of these parasites, and washed off, rendered the soil with which it intermixed capable of retaining moisture, while the trunks of the trees prevented the rains from running off, thus giving rise to a marsh—a condition of the surface favouring the growth of mosses, which speedily took possession of it, and ultimately produced the peat.

Vast peat districts occur abundantly in France, the Netherlands, Germany, Russia, the Canadas, Scotland, and Ireland, and are found in insulated situations in Iceland, the Shetlands, and the Falkland Islands. Ireland has such extensive formations, owing to the prevailing humidity and low temperature of the climate. They occupy nearly onetenth of the surface; or, excluding some small mountainous and detached patches, the total quantity of bog has been estimated at 2,831,000 acres, of which 1,576,000 acres are flat red bog, capable of being reclaimed, and 1,255,000 are mountain bog, mostly convertible into pasture land. A single bog on the Shannon-that of Allen-extends fifty miles in length, by from two to three in breadth; while the great peat marsh of Montoire, near the mouth of the Loire, has a circumference of fifty leagues. The beds, in some instances, have been dug into to the depth of twenty feet, and even to twice that thickness; but such in general is their spongy nature, that a mass may usually be reduced by compression to about one-fifth of its original thickness. The rate at which a peat bog or moss advances varies so much under different circumstances, that we are precluded from forming any certain estimate of the antiquity of a formation, otherwise than from data supplied by imbedded animal and human relics. The coins of Gordian found in the peat at Groningen, and the Roman axes discovered in the peat of Yorkshire, throw light

upon the date of those deposits. In the Irish bogs it is very common to find the remains of animals of which no living specimens now exist in that country, nor have existed within the era of authentic history-horns and skulls of the elk and deer-so that their age goes back to a remote period.

Peat-mosses have long been remarked for their antiseptic properties, or the power of preserving animal substances from putrefaction; some striking instances of which are on record. Two human bodies, buried in moist peat, in Derbyshire, in 1674, about a yard below the surface, were found, nearly twenty-nine years afterwards, with the colour of the skin fair and natural, and the flesh as soft as that of persons newly deceased. In June 1747, a Lincolnshire labourer, digging peat on one of the moors, discovered the body of a woman, a lady of the olden time, at the depth of six feet. The head and feet were nearly bent together, and the skin, nails, and hair were in a high state of preservation. She wore leathern shoes or sandals, each cut out of a single piece of tanned oxhide, folding about the foot and heel, and piked with iron. Chaucer mentions these piked shoes as part of the costume in his time; and in the reign of Edward IV. they had so increased in length, that all who wore them beyond a certain length were to be mulcted, or have them cut shorter, in passing in or out of the city gates of London. For several centuries, therefore, the body had certainly lain in the peat.

We have mentioned the semi-fluid condition of many peat-mosses below the surface crust, giving them a motion like that of a boat in water when subject to pressure. Hence, when overcharged in consequence of excessive rains, these swollen mosses have not unfrequently burst; and when occupying a high situation or declivity, their contents have been discharged with great violence upon a lower level, like a current of lava streaming from a volcano. Several cases of these inundations have occurred in recent times, the most remarkable of which transpired on the 16th of December 1772, in the instance of the Solway moss. This moss, already noticed as having entombed a troop of horse, occupied an area of 1300 acres, stretching along an eminence elevated from fifty to eighty feet above the fertile plain between it and the river Esk. The surface, of some consistency, vibrated to the tread, and might be easily pushed through with a pole, which descended without difficulty from fifteen to twenty feet, showing the soft and watery state of the subjacent matter. After greater rains than had happened for nearly two centuries, the surface of the moss rose, owing to the waters accumulated in it not being able to find a vent, and at length broke, discharging itself upon the hapless valley of the Esk, an entirely new phenomenon in the life of its simple shepherds. What added to their terror and danger was the hour of the eruption, about eleven on the night of the 15th, when the inhabitants of the farms and hamlets of Eskdale had retired to their beds. Some were awakened by the strange noise of the eruption; others by the cry of alarm which speedily rang through the valley; and all awoke from their sleep to encounter in their cottages, or immediately upon opening their doors, a slowly rolling, resistless, and inexplicable deluge of black mud. The members of thirty-five families saved their lives with difficulty, but lost their agricultural produce, with many of their cattle; and when the morning shed light upon the scene, instead of fields, hedge-rows, and cottage gardens, there was a dark slimy torrent of half-consolidated peat earth, almost wholly covering some of the houses, and reaching up to the thatch of others. About four hundred acres were buried; and but for the crawling motion of the semi-solid mass, and the occurrence of an intervening "gap" or broad gully, which diverted into an opposite direction a large quantity of the invading matter, but few of the Eskdale shepherds would have survived the calamity. Though these sudden inroads are few and far between, yet the peat-mosses steadily advance in extent and thickness by natural increase, where the conditions essential to their growth remain unaltered; and in a series of years great changes are effected