THE CHAIN OF CAUSES.

'IT is no recent discovery,' says an ingenious French writer of the last century, 'that there is no effect without a cause, and that often the smallest causes produce the greatest effects. Examine the situations of every people upon earth;—they are founded on a train of occurrences seemingly without connexion, but all connected. In this immense machine all is wheel, pulley, cord, or spring. It is the same in physical nature. A wind blowing from the southern seas and the remotest parts of Africa brings with it a portion of the African atmosphere, which, falling in showers in the valleys of the Alps, fertilizes our lands. On the other hand, our north wind carries our vapours among the negroes: we do good to Guinea, and Guinea to us. The chain extends from one end of the universe to the other.' Waiving, however, for the present, the moral view of the question, I may be permitted to present my readers with an illustration of the physical one,-i.e., the dependence of the conditions of one country on the conditions on which some other and mayhap very distant country exists, which may be new to some of them, and which the Frenchman just quoted could have little anticipated.

When in the island of Bute, to which I had gone on two several occasions in the course of a few weeks, in order to examine what are known to geologists as the Pleistocene deposits of the Kyles, my attention was directed to a deep

excavation which had just been opened for the construction of a gas tank in the middle of the town of Rothesay. It was rather more than twenty feet in depth, and passed through five different layers of soil. First, passing downwards, there occurred about eighteen inches of vegetable mould, and then about seven feet of a partially consolidated ferruginous gravel, which rested on about eighteen inches more of peat moss, -once evidently a surface soil, like the overlying one, though of a different character,—abounding in what seemed to be the fragments of a rank underwood, and containing many hazel-nuts. Beneath this second soil there lay fully nine feet of finely stratified sea-sand; and under all, a bed of arenaceous clay, which the workmen penetrated to the depth of about two feet, but, as they had attained to the required depth of their excavation, did not pass through. And this bed of clay, at the depth of fully twenty feet from the surface, abounded in sea-shells,-not existing in the petrified condition, but, save that they had become somewhat porous and absorbent, in their original state. Not a few of them retained the thin brown epidermis, unchanged in colour; and the gaping and boring shells, whose nature it is to burrow in clay and sand, and which were present among them in two well-marked species, occupied, as shown by their position, the place in which they had lived and died. Now, of these ancient deep-lying shells, though a certain portion of them could be recognised as still British, there were proportionally not a few that no longer live within the British area ;—in vain might the conchologist cast dredge for them in any sea that girdles the three kingdoms; and the whole, regarded as a group, differed from any other that exists in Europe in the present day. Ere, however, I pass on to decipher the record which they form, or translate into words the strange old prehistoric facts with which they are charged, let me briefly refer to the overlying deposits, and the successive periods of time which they seem to represent.

X

The upper layer of vegetable mould here fully exhausts the historic period. And yet the fine old town of Rothesay is not without its history. The ancient ivy-clad castle of the place is situated scarce a minute's walk from the excavation; the same stratum of vegetable mould lies around that forms the upper layer in the pit, furnishing rich footing to shrub and tree; and its green moat, deserted long since by the waters, was excavated of old in the ferruginous gravel. And yet, though compared with the age of the gravel-bed on which it stands, the date of its erection is as of yesterday: history fails to trace its origin: we only know that it was already an important stronghold in the days of Haco of Norway, one of whose captains besieged and took it,

that Robert III. of Scotland died broken-hearted within its walls,—and that it still furnishes with his second title the heir-apparent of the British throne. On many other parts of the coast, though apparently not here, this gravel-bed contains shells, all of which, unlike those of the arenaceous clay beneath, still live around our shores, and most of which occurred, ere the last upheaval of the land, as dead shells on the beaches of the old coast line. The old line itself, against which the sea seems to have stood for ages ere the final upheaval, is present here immediately behind the town, in an eminently characteristic form. Its precipices of rough conglomerate still exhibit the hollow lines, worn of old by the surf, and occupy such places in relation to the buildings below as prove that even the oldest erections of the town, with the first beginnings of the castle, were all raised on one of its wave-deserted beaches. But the annals of Rothesay, notwithstanding their respectable antiquity, or even such memorials of human origin in the neighbourhood as altogether extend beyond the memory of history, advance comparatively but a little way towards the period of the old coast line and the last upheaval. When, in the times of Julius Cæsar, Diodorus Siculus wrote his big gossiping

history, St. Michael's Mount, in Cornwall, was connected. with the mainland at low water as it is now, a fact good in evidence to show that since that age the respective levels of land and water have not altered in Britain. The old coast line must have been already upheaved when Cæsar landed in the island. And yet, though, as shown by its profound caves and deeply excavated hollows, the sea must have beaten against it during an immensely protracted period of depression, there existed a previous period of upheaval, represented by the layer of moss at the bottom of the gravel, when the land must have stood considerably higher over the sea-level than it does now. In many localities around the shores of Britain and Ireland, the moss-bed which so often underlies the bed of old coast gravel is found to run out under the sea to depths never laid bare by the tide; and yet at least as low as the sea ever falls, it is found bearing its stumps and roots of bushes and trees of existing species, that evidently occupy the place in which they had originally grown and decayed. These submerged mosses, as they are termed, occur along the sides of the Firths of Tay and. Forth, and in at least one locality on the southern side of the Moray Firth; on the west coast they lie deep in lochs and bays; they occur on various parts of the coasts of Ireland; and off the shores of Erris and Tyrawly have furnished a basis for strange legends regarding an enchanted land, which once in every seven years raises its head above the water, green with forests and fields, but on which scarce any one has succeeded in landing. They occur also on the English shores, in one interesting instance in the immediate neighbourhood of that St. Michael's Mount, which, from the description of the Sicilian historian, furnishes a sort of negative measure of the period during which the gravel bed immediately over them was elevated. 'On the strand of Mount's Bay, midway between the piers of St. Michael's Mount and Penzance, on the 10th of January 1757,' says

Borlase, in his Natural History of Cornwall, 'the remains of a wood, which anciently must have covered a large tract of ground, appeared. The sands had been drawn off from the shore by a violent sea, and had left several places, twenty yards long and ten wide, washed bare, strewed with stones like a broken causeway, and wrought into hollows somewhat below the rest of the sands. This gave me an opportunity of examining the following parts of the ancient trees :-In the first pool part of the trunk appeared, and the whole course of the roots, eighteen feet long and twelve wide, were displayed in a horizontal position. The trunk at the fracture was ragged; and beside the level range of the roots which lay round it was part of the body of the tree, just above where the roots divided. Of what kind it was there did not remain enough positively to determine. The roots were pierced plentifully by the teredo or auger worm. Thirty feet to the west we found the remains of another tree: the ramifications extended ten feet by six; there was no stock in the middle; it was therefore part of the under or bottom roots of the tree, pierced also by the teredo, and of the same texture as the first. Fifty feet to the north of the first tree we found part of a large oak; it was the body of a tree three feet in diameter; its top inclined to the east. We traced the body of this tree, as it lay shelving, the length of seven feet; but to what further depth the body reached we could not discern, because of the immediate influx of water as soon as we had made a pit for discovery. It was firmly rooted in earth six inches from the surface of the sand: not so fixed was the stock of a willow tree, with the bark on, one foot and a half in diameter, within two paces of the oak. The timber was changed into a ruddy colour; and hard by we found part of a hazel-branch, with its glossy bark on. The earth in all the tried places appeared to be a black, cold marsh, filled with fragments of leaves of the Juncus aquaticus maxi