CUMULOSE DEPOSITS 305 



drained, may be made extremely fertile, though in periods of 

 drought endangered by fire which, onee started, may burn for 

 months, doing immense damage. The partially reclaimed areas 

 of the Great Dismal Swamp of Virginia are fairly representative 

 types of swamp soils. 



The formation of eumulose deposits is not, however, limited 

 to lakes, stagnant ponds, or even to swamps as the word is ordi- 

 narily used, excepting as the swamp itself may be incidental 

 and consequent. Regions of poor drainage, particularly in 

 moist and cool climates, may give rise to growths of sphagnous 

 mosses and subsequently to plants of a higher type, which in 

 course of years assume no insignificant proportions. 



In accounting for such accumulations, we have but to remem- 

 ber that ordinarily when a plant dies, its organic constituents 

 are returned to the atmosphere once more in a comparatively 

 brief period of time through the usual processes of decay. It 

 needs only such conditions of moisture as shall prevent com- 

 plete decay and hence favor the accumulation of the organic mat- 

 ter, to give rise to beds of peat and ultimately of coal. Plants 

 of the type of sphagnous mosses, growing continuously above 

 and dying beneath, hold in their mass sufficient moisture to 

 exclude atmospheric air, and thus themselves bring about the 

 proper conditions for bog making. In virtue of this property 

 such bogs may gradually rise above the level of the surrounding 

 country, as is the case with the Great Dismal Swamp of Vir- 

 ginia and numerous others that need not be mentioned here. 

 Instances are on record where bogs of this nature have grown 

 so far above the natural level, that during seasons of unusual 

 rainfall they have burst, and flooded adjacent regions, with dis- 

 astrous results. The rate of growth of such accumulations is 

 naturally quite variable. H. S. Gesner, as quoted by T. Rupert 

 Jones,^ states that in Bavarian moors the observed increase in 

 peat, in forty-five years, amounted to from 2 to 3 feet in thick- 

 ness; in Oldenberg, in one hundred years, to 4 feet; in Ham- 

 melsmoor, Denmark, to 2-| feet ; and in Alpine districts to 4 and 

 5 feet in from thirty to fifty years. 



The peat bogs, so characteristic of Ireland, Scotland, and 

 other northern latitudes, are of this type. A section of the 



^Proc. Geologists' Association, Yol. VI, No. 5, January, 1880. 

 21 



