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Page:Popular Science Monthly Volume 70.djvu/564

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564
THE POPULAR SCIENCE MONTHLY

ried down through the superficial deposits to a clay formation, which is presumably of Pleistocene age, and this clay formed the foundation for the tan vats located in the surface stratum. The excavations disclosed numerous, scattering fragments of leather and tan bark, sufficiently ample to make the former use of the locality quite manifest; but nowhere were there any local accumulations of a nature or in such quantity as to explain the formation of gas in any appreciable volume. Moreover, had gases formed there they would most naturally have worked upward through the permeable soil and thus they would have escaped directly into the atmosphere rather than have taken a seemingly impossible course down a slope for a distance of some two hundred feet or more. It is, moreover, about eighty years since tanning operations were carried on in that locality, and the conditions of the soil render it unlikely that any very large amount of gas could be stored there for that length of time. The theory that the gases had their origin in the decomposing organic debris of a tan-yard must therefore be dismissed as untenable.

2. The Atlantic coast line, probably throughout its entire extent, is undergoing depression at the rate of about two feet per century. This leads to a variety of well-defined changes, among which may be mentioned the gradual silting up of protected areas, the submergence and final burial of forests and the formation of marsh lands. Nowhere are these changes better exemplified than in the neighborhood of Eye in New Hampshire, and Kittery and York in Maine, for the reason that they are developed within areas of such size, and within periods of such short duration, as to be brought well within the experience of individual observers.

Wherever silting occurs, and more particularly where marsh lands are formed, large volumes of gas are generated and may be readily observed rising to the surface of the water at more or less frequent intervals. In the case of the silted areas the gas is obviously the product of vast quantities of Zostera, supplemented by other forms of organic remains, both plant and animal. In the marsh lands the gas is the normal end product in the decay of the lower portions of the marsh turf. This gas generally accumulates in the turf and in the silt below, sometimes being held in pockets in such large volume that when suddenly liberated its effects are overpowering. For one who is at all acquainted with such marsh lands it is not difficult to reach an explanation as to the production of gas in sufficient volume and of the proper kinds to produce all the phenomena under consideration. It was therefore felt that there might be a small, buried marsh beneath the beach at Kittery Point, and an attempt was made to solve the question by direct examination, with the following results:

For a depth of about seven inches the beach consists of a fine and compact sand worked into a layer of great firmness. Below this, as far down as it was possible to go without the use of special methods,