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 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. At 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 thechannels, 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 steadyrapidity 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 ancientFOOT-PRINTS OF ANIMALS ON A SLAB OF STONEtraces, 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 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 obser ve 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 aspace 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, thatan inferior layer,deposited perhaps ten or fourteen tides previously, exhibits on its under surface perfect casts of rain-printswhich stand out in relief, the moulds of thesame being seen in the layer below."FOOT-PRINTS OF BIRDSON A SLAB OF STONE
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 windingtubular 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 thefoot-prints of birds, and of musk-rats, minks,dogs, sheep, andcats. The leaves also of elm, maple, and oak trees have beenscattered 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 sun-cracks 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.
- From DAWSON"S Acadian Geology
To what does the vertical rise of the tide in the Bay of Fundy amount? What appearance does the coast present at low-tide? What has the torrent of red water often in its front? What does the stranger feel as he sees its advance? For what does the sediment in the Bay of Fundy afford facilities? What do these appearances illustrate? Why is the sediment extremely fine? At what time are large areas of it exposed to the sun? What portion of it is best adapted for receiving impressions? Of what did Lyell find casts between the layers? Of what are these perfect instances? What is inferred from the presence of stumps of trees rooted in the soil?
