56o 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, suf- 

 ficiently 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 seem- 

 ingly impossible course down a slope for a distance of some two hun- 

 dred 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. No- 

 where are these changes better exemplified than in the neighborhood of 

 Eye in New Hampshire, and Kittery and York in Maine, for the rea- 

 son that they are developed within areas of such size, and within 

 periods of such short duration, as to be brought well within the experi- 

 ence 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 prod- 

 uct of vast quantities of Zostera, supplemented by other forms of or- 

 ganic 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, 



