STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 113 



dunes have covered great portions of the peat area, while other great 

 portions have remained uncovered and in continuous growth. 



8. Expansion of peat deposits by transgression has been observed 

 in all parts of the world. Trees, still standing but killed by advanc- 

 ing marshes, have been described by several writers in the United 

 States, and the process of covering the stems has been made clear 

 in preceding pages by citations from Scottish authors. In many 

 deposits of wide extent, the fact of transgression becomes evident 

 only after removal of the peat for fuel or during reclamation. The 

 stumps of the invaded forest are laid bare, their roots still fixed in 

 the mur of the deposit, while their broken and shattered trunks are 

 prostrate in the peat, which accumulated around the trees and de- 

 stroyed them by preventing aeration of the roots. JNIany of these 

 great deposits have no trees rooted in the mur in some portions, 

 while those are abundant in other portions. The stumpless spaces 

 mark the places where the bog originated; those with stumps and 

 prostrate stems mark expansion by transgression on the forest area. 

 These features are characteristic of peat deposits in the British Isles, 

 the Netherlands, France, Germany, Sweden as well as of those East 

 Indian swamps which have been reclaimed for agricultural purposes. 



9. The effect of pressure on peat is to render it so similar physi- 

 cally to brown coal that the contrast with normal peat is very great. 

 Forchhammer, Jentzsch, Nilson, Lesquereux, Goeppert and Schreiber 

 have w^ritten in detail respecting this matter and incidental observa- 

 tions are to be found in writings by other authors. Even the long- 

 continued pressure of peat itself in a deep deposit has much the same 

 effect on the lowest layers. 



10. Peat contains introduced materials of various kinds. Logs 

 and stumps are not of these ; they are merely the more resistant 

 parts of peat-making plants, embedded in pulp from less resistant 

 portions. Fragments of rock, sometimes angular, sometimes water- 

 worn, have been reported from a few localities. The comparative 

 infrequency of references may indicate rarity of occurrence, localiza- 

 tion within the peat or the indifference of observers. The facts avail- 

 able are so few that any suggestion as to the origin of these frag- 

 ments would be worthless. Often, there is much silt; at times, one 



