Page:Popular Science Monthly Volume 23.djvu/555

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A NATURAL SEA-WALL.

water. After a severe storm the road is sometimes strewed thickly with these great pebbles, and some trouble is necessary to clear it. So, at least, says popular tradition, but it is probable that very many of the larger stones, found some rods inland, were deposited there before the wall existed in anything like its present condition. For it is almost certain, from the character of the formation and its known history, that it has been piled up in comparatively recent times.

Some of the old inhabitants assert that the terrific storm that in 1851 devastated the whole New England coast and snapped like pipe stems the iron pillars of the Minot's Ledge light-house, is responsible, too, for the wall. While that noted storm certainly did perform some tremendous feats, and in some places permanently changed the contour of the shore, no one storm could do its work in a very systematic or regular fashion. No one storm could have formed the three terraces that compose the sea-face of our wall. The Minot's Ledge storm may have greatly augmented an existing pile and changed its shape somewhat (as there is reason to believe it did), but, powerful as it was, it did not do anything more than this.

It is said that the above-mentioned storm so blockaded the existing highway that it was moved a short distance inland, and there is evidence to show that this road once ran near the present high-water mark, on or about the line now occupied by the wall.

It is, then, probable that a double process has been going on. The sea has been encroaching on the beach, and at the same time obstructing its own course with the d├ębris of former invasions. It is worthy of notice that the wall has only been thrown up along the sandy beach, where the waves had an unobstructed passage. On the ledges that are of frequent occurrence no signs of any extensive deposit are visible. The wall is absent or much modified where a shoal intervenes. These facts show that the deposit has been the result of successive storms heaping up the material, and the ordinary course of the waves and tides molding and arranging it. When the angle of the pile exceeded the natural slope of such materials, growth in that particular plane ceased, and a terrace was formed. Thus the wall, as far as its seaward side is concerned, seems to be a sort of concretion, the terraces being formed in succession, partly out of new material furnished by annual storms and partly from what was left after the first terrace had reached its present angle. Constant pounding of the waves has solidified the wall, though various storms have partially undermined it and necessitated the re-formation of its face. To these storms is due the motion landward that has from time to time taken place. The materials of the wall have been collected from a large area, as is shown by their diverse character, and why they should have been deposited at this particular point is a matter of some doubt. It may be that submarine ledges off this part of the coast have furnished a quarry for the waves. The method of formation, however, has