648 Natural History of Nova Scotia, 



kind of wood sinks after remaining a certain time in the water. 

 The leaves constantly falling in are never returned to the 

 land. Vegetable substances embedded in mud, under water, 

 are remarkably durable. I have taken up a stick of white 

 birch from a beaver pond, which, from the growth of wood 

 on the site of the house, I judged, must have been em- 

 bedded for near a century. Neither the bark nor the wood 

 was distinguishable from those of a green tree. Yet the 

 inner bark of this tree decays in one summer when exposed 

 to the air. Heavy rains, which send torrents of water into 

 the swamps, make a small addition to the material of the 

 bogs ; but it is but a small one while the forest is growing. 

 On a barren soil, the surface is entirely covered with a rough 

 coat of vegetation. Even where the spruce is so thick as to 

 suffocate the shrubs and perennial plants, the ground is co- 

 vered with a fleece of dry moss, which, like a strainer, retains 

 every thing that can form turf. The brooks on this soil, 

 however rapid they may be, have low banks, and are hardly 

 perceived to wear away any portion of the earth. They run 

 upon beds of stones, which are themselves prevented from 

 attrition by the water moss and byssus which cover them ; 

 the dead leaves, twigs, and scales of bark, which fall into the 

 streams, do not go far before they are arrested by the fallen 

 trees which cross the brooks, forming little patches of swamp 

 where the banks are low. But it is after every fire that runs 

 through the woods, that large additions are made to the de- 

 posits of peat earth. Very extensive fires in the woods are 

 so generally followed by heavy floods of rain, that there is 

 some reason to think that the enormous pillars of smoke have 

 some share in producing them. The water now rushes over 

 a surface smoothed by the fire, and carries with it into the 

 swamps and ponds considerable quantities of charcoal, frag- 

 ments of turf, spruce cones, pieces of the outer bark of trees 

 and shrubs, and other light substances; among which the 

 shining shells of coleopterous insects are very perceptible, in 

 quantities fully sufficient to account for the ammonia which 

 is yielded by pit coal, if coal is formed, as seems probable, from 

 antediluvian deposits of vegetable matter. The mud accu- 

 mulated in lakes and ponds is prevented from passing into the 

 sea by aquatic plants. The bottoms of muddy lakes have a 

 thick growth of water grass wherever the water is about 6 ft. in 

 depth ; the shallows are occupied by water lilies [nine species 

 inhabit North America], Sagittaria, and other plants, among 

 which the Pontederm, which produces such large spikes of 

 blue flowers, is the most remarkable. 



The byssus (the green slimy plant that is so common in 



