STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 117 



when it grows in a swamp, wJiere the roots are in the saturated peat, 

 covered with water, it puts forth the curious " knees," which 

 project beyond the water surface and provide means for aeration. 

 If the water-level be changed abruptly, so that the knees are sub- 

 merged, the tree dies, as appears in the New Madrid area, where 

 during the earthquake of 1811, the land sank and the swampy area 

 became a lake. Nyssa is provided with an equivalent protection 

 for aeration. Conifers are found far out on the wet sedge-mat, 

 which floats on the surface of a lake ; but they grow slowly amid the 

 untoward conditions and usually are overturned by the wind before 

 attaining great size, as their roots are radial and very near the 

 surface. Capp's observations respecting conditions in the White 

 river district of Alaska are thoroughly illustrative. Peat as a soil 

 is not repugnant to plants. The acid character of new peat is 

 offensive to most of our deciduous trees and to many other plants; 

 but many others, among them majestic trees both conifer and 

 deciduous, thrive best on the damp acid material. When a bog 

 ceases to grow, the thin upper layer becomes freed in considerable 

 measure from the acid and the moisture ; usually it is occupied 

 quickly by the ordinary forest trees of the region, though the 

 saturated peat may be only a foot below. The roots of these trees 

 are radial, creeping near the surface. 



15. Peat, deprived of moisture and exposed to the air, quickly 

 undergoes change. The soluble cementing material becomes in- 

 soluble, or is removed, the mass becomes pulverulent and is apt 

 to be swept away by the wind. The vast reclamation works, which 

 have converted swamp areas into agricultural land, have e?^hibited 

 the changes on a grand scale. The natural conclusion seemed to 

 be that peat has been formed only to waste away. But this is an 

 error. Peat has been formed to be preserved. Peat deposits in 

 Scandinavia, Germany and Great Britain have existed since the 

 Glacial period and in not a few localities they are still growing. 

 But the growth has been interrupted many times and for consider- 

 able periods ; the surface was exposed, but not long. Under ordi- 

 nary conditions, shrubs and trees advance as the peat surface dries 

 and the Waldmoor or forested bog is protected from waste. Under 



