36 JEAN DAWSON 



were all dead and their shells crumbled when touched. This 

 dearth of life is attributed to the great amount of vegetable 

 mould collected upon and beneath the moss. The inwash 

 from the ploughed fields covers the peat with a coating of heavy 

 clay to a depth of six or eight inches leaving no surface trace of 

 either plant or animal life. 



Group C is the last of the series and represents the latest 

 stages of swamp life. 



Group C — Swamp C ^ This little swamp or pond is sur- 

 rounded by a hay field and is wholly cleared, with no trees or 

 bushes growing in or around it. The substratum is of stiff 

 blue clay and it has no water plants except some traces of algae 

 and a moderate growth of Alisnia plantago L. The clay covers 

 the whole swamp bed, no traces of peat are seen, which is due 

 perhaps to the rapid deposition of clay, eroded from the sur- 

 rounding clay hills. 



The cla,y in the bed of the swamp is so dry that cracks from 

 eight to eighteen inches in depth and from two to three and a 

 half inches in width are found, caused by the long continued 

 drought of the summer and early fall. Imbedded in this clay 

 were hundreds of shells of Lymnaea palustris and two dead shells 

 of Physa gyrina hildrethiana. 



A portion of this clay with its imbedded shells, from one 

 of the many tiny depressions of the saucer-like basin of the 

 swamp is showna in Fig. lo. The shells are well scattered over 

 the whole area, but more are in the center of these depressions, 

 where, no doubt, the water lingered longer than in the some- 

 what higher portions. Nearly all of the more recent shells 

 which had their apertures well sealed in the clay were alive 

 and revive in a short time after being placed in water. All 

 of these living shells that were sealed in the clay had a mucous 

 epiphragm over the aperture. A careful study of the shells 

 for the presence of a habit of burrowing into the soil, to in- 

 sure the closure of the aperture in case of drought, revealed 

 no indication whatever of such a habit. There w^ere about 

 as many shells with the aperture sealed in the clay as of those 

 with the aperture exposed. All of the fresh shells that were 

 sealed in the clay were alive, but there were also some old dead 

 shells which were fairly well sealed ; however, it was thought 

 that perhaps the water of the previous season washed the clay 



