THE TIDE-WAVE IN THE BAY OF FUNDY:
ITS GEOLOGICAL VALUE.

JOHN WILLIAM DAWSON, LL.D., F.R.S. (b. 1820), Principal of
M'Gill University, Montreal.

The tide-wave that sweeps to the north-east, along the Atlantic coast of the United States, entering the funnel-like mouth of the Bay of Fundy, becomes compressed and elevated as the sides of the bay gradually approach each other. In the narrower parts, the water runs at the rate of six or seven miles an hour, and the vertical rise of the tide amounts to sixty feet or more! At some points these tides, to an unaccustomed spectator, have rather the aspect of some rare convulsion of nature than of an ordinary daily occurrence.

At

At low tide, wide flats of brown mud are seen to extend for miles, as if the sea had altogether retired from its bed; and the distant channel appears as a mere strip of muddy water. the commencement of flood, a slight ripple is seen to break over the edge of the flats. It rushes swiftly forward, and, covering the lower flats almost instantaneously, gains rapidly on the higher swells of mud, which appear as if they were being dissolved in the turbid waters.

At the same time the torrent of red water enters all the channels, creeks, and estuaries; surging, whirling, and foaming, and often having in its front a white, breaking wave, or "bore, which runs steadily forward, meeting and swallowing up the remains of the ebb still trickling down the channels. The mud flats are soon covered; and then, as the stranger sees the water gaining with noiseless and steady rapidity on the steep sides of banks and cliffs, a sense of insecurity creeps over him, as if no limit could be set to the advancing deluge. In a little time, however, he sees that the fiat, “Hitherto shalt thou come, but no further," has been issued to the great bay tide: its retreat commences, and the waters rush back as rapidly as they entered.

Much interest attaches to the marine sediment of the Bay of Fundy, from the great breadth of it laid bare at low tide, and the facilities which it in consequence affords for the study of sun-cracks, impressions of rain-drops, foot-prints of animals, and other appearances which we find imitated on many ancient rocks. The genuineness of these ancient traces, as well as their mode of preservation, can be illustrated and proved only by the

study of modern deposits. We quote a summary of facts of this kind from a paper on Rain-prints by Sir Charles Lyell, who was the first to direct attention

SLAB OF STONE.

to these phenomena as exhibited in the Bay of Fundy.

"The sediment with which the waters are charged is extremely fine, being derived from the destruction of cliffs of red sandstone and shale, belonging chiefly to the coal measures. On the borders of even the smallest estuaries communicating with a bay in which the tides rise sixty feet and upwards, large areas are laid dry for nearly a fortnight, between the spring and the neap tides; and the mud is then baked in summer by a hot sun, so that it becomes solidified and traversed by cracks. Portions of the hardened mud may then be taken up and removed without injury.

"On examining the edges of each slab, we observe numerous layers, formed by successive tides, usually very thin-sometimes only one-tenth of an inch thick; of unequal thickness, however, because, according to Dr. Webster, the night tides, rising a foot higher than the day tides, throw down more sediment.

"When a shower of rain falls, the highest portion of the mud-covered flat is usually too hard to receive any impressions; while that recently uncovered by the tide, near the water's edge, is too soft. Between these areas a space occurs almost as smooth and even as a looking-glass, on which every drop forms a cavity of circular or oval form. If the shower be transient these pits retain their shape permanently, being dried by the sun, and being then too firm to be effaced by the action of the succeeding tide, which deposits upon them a new layer of mud. Hence we find, on splitting open a slab an inch or more thick, on the upper surface of which the marks of recent rain occur, that an inferior layer, deposited perhaps ten or fourteen tides

previously, exhibits on its under surface perfect casts of rainprints which stand out in relief, the moulds of the same being seen in the layer below."

After mentioning that a continuous shower of rain obliterates the more regular impressions, and produces merely a blistered surface, Sir Charles adds:

"On some of the specimens there are seen the winding tubular tracks of worms, which have been bored just beneath the surface. Sometimes the worms have dived, and then reappeared. Occasionally the same mud is traversed by the foot-prints of birds, and of muskrats, minks, dogs, sheep, and cats. The leaves also of elm, maple, and oak trees have been scattered by the winds over the soft mud, and, having been buried under the deposits of succeeding tides, are found on dividing the layers. When the leaves themselves are removed, very faithful impressions, not only of their outline, but of their minutest veins, are left imprinted on the clay."

We have here a perfect instance, in a modern deposit, of appearances which we notice in some of the most ancient rocks; and it is only by such minute studies of existing nature that we can hope to interpret those older appearances. In some very ancient rocks we have impressions of rain-marks quite similar to those which occur in the alluvial mud of the Bay of Fundy. In those old rocks, also, and especially in the coal formation, we find surfaces netted with suncracks precisely like those on the dried surfaces of the modern mud flats, and faithful casts of these taken by the beds next deposited.

A striking geological fact connected with the marshes, is the presence beneath them of stumps of trees still rooted in the soil, and other indications which prove that much, if not the whole of this marine deposit, rests on what once was upland soil supporting forest trees; and that, by some change of level,

these ancient forests had been submerged and buried under the tidal deposits. Acadian Geology, 3rd ed., 1878.

HOW COAL IS MADE.

REV. CHARLES KINGSLEY (1819-1875).

When it was first seen that coal had been once vegetable, the question arose, How did all these huge masses of vegetable matter get there? The Yorkshire and Derbyshire coal-fields, I hear, cover seven hundred or eight hundred square miles, the Lancashire about two hundred. How large the North Wales and the Scotch fields are I cannot say. But doubtless a great deal more coal than can be got at lies under the sea, especially in the north of Wales. Coal probably exists over vast sheets of England and France, buried so deeply under later rocks that it cannot be reached by mining. As an instance, a distinguished geologist has long held that there are beds of coal under London itself, which rise, owing to a peculiar disturbance of the strata, to within one thousand or one thousand two hundred feet of the surface, and that we or our children may yet see coal-mines in the marshes of the Thames. And more: it is a provable fact that only a portion of the coal-measures is left. A great part of Ireland must once have been covered with coal, which is now destroyed. Indeed, it is likely that the coal now known of in Europe and America is but a remnant of what has existed there in former ages, and has been eaten away by the inroads of the

sea.

Now whence did all that enormous mass of vegetable soil come? From some neighboring land, was the first and most natural answer. It was a rational one. It proceeded from the known to the unknown. It was clear that these plants had grown on land, for they were land-plants. It was clear that there must have been land close by, for between the beds of coal, as you all know, the rock is principally coarse sandstone, which could only have been laid down in very shallow water.

It was natural, then, to suppose that these plants and trees had been swept down by rivers into the sea, as the sands and muds which buried them had been. And it was known that at the mouths of certain rivers-the Mississippi, for instance— vast rafts of dead floating trees accumulated; and that the bottoms of the rivers were often full of snags, etc., trees which

had grounded and stuck in the mud; and why should not the coal have been formed in the same way?

Because-and this was a serious objection-then surely the coal would be impure, mixed up with mud and sand till it was not worth burning. Instead of which, the coal is usually pure vegetable, parted sharply from the sandstone which lies on it. The only other explanation was, that the coal vegetation had grown in the very places where it was found. But that seemed too strange to be true, till that great geologist, Sir W. Logan, who has since done such good work in Canada, showed that every bed of coal had a bed of clay under it, and that that clay always contained fossils called stigmaria. Then it came out that the stigmaria in the under clay had long filaments attached to them, while, when found in the sandstones or shales, they had lost their filaments, and seemed more or less rolled; in fact, that the natural place of the stigmaria was in the under clay. Then Mr. Binney discovered a tree-a sigillaria-standing upright in the coal-measures with its roots attached. Those roots penetrated into the under clay of the coal, and those roots were stigmarias. That seems to have settled the question. The sigillarias, at least, had grown where they were found, and the clay beneath the coal-beds was the original soil on which they

had grown. Just So, if you will look at any peat-bog, you will

find it bottomed by clay, which clay is pierced everywhere by the roots of the moss forming the peat, or of the trees-birches, alders, poplars, and willows-that grew in the bog. So the proof seemed complete that the coal had been formed out of vegetation growing where it was buried. If any further proof for that theory was needed, it would be found in this fact, most ingeniously suggested by Mr. Boyd Dawkins:-The resinous spores or seeds of the lepidodendra made up a great part of the bituminous coal. Now those spores are so light, that if the coal had been laid down by water they would have floated on it, and have been carried away; and therefore the bituminous coal must have been formed, not under water, but on dry land.

If, therefore, the reader wishes to picture to himself the scenery of what is now central England during the period when our coal was being laid down, he has only, I believe, to transport himself in fancy to any great alluvial delta, in a moist and warm climate favorable to the growth of vegetation. He has only to conceive wooded marshes at the mouth of great rivers slowly