116 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



one peat horizon and the next. Very often one finds in this interval 

 alternation of land, freshwater and marine conditions. The immedi- 

 ate roof may be clay succeeded by sand, both of freshwater origin, 

 but on these may rest sand or marl with shells of familiar marine 

 mollusks. The sands frequently contain transported remains of 

 plants, in some cases trunks of trees, prostrate, inclined or even 

 approaching the vertical and accompanied at times by bones of vari- 

 ous mammals, with land, freshwater or brackish water shells. The 

 plant remains usually differ from those in the peat, and they appear 

 to have come from undermined banks of rivers. An interesting and 

 by no means uncommon feature is the occurrence of " soils of vege- 

 tation," bearing remains of forest growth, there being an accumula- 

 tion of forest offal about and between the stumps. These mark ex- 

 posed surfaces on which trees grew but where swampy, peat-forming 

 conditions did not prevail. Erect as well as prostrate trunks are 

 present, all enveloped by the mass of sand or clay which buried the 

 old soil. 



13. All areas in which peat accumulates have imperfect drain- 

 age ; the streams are usually sluggish and are easily diverted. The 

 peat, at times, encroaches on the channelways and eventually fills 

 them. This condition is recognized readily v^^hen the section is ex- 

 posed in excavations for reclamation canals, for the silt or sand 

 forms a " roll " on the bottom, narrowing upward and covered by 

 peat. Sometimes a new channel is formed during a flood and the 

 sand-laden water tears away the peat, sometimes to the bottom, giv- 

 ing a " roll " in the roof, which narrows downward. Similar condi- 

 tions are not rare in interval rocks between peat horizons, buried 

 channelways being of frequent occurrence. This contemporaneous 

 erosion marks the existence of land surfaces. 



14. Plants growing on peat show great adaptability to changing 

 conditions. Birch requires that the roots have free access to air, 

 but C. A. Davis states that he has seen birch making thrifty growth, 

 where the roots had been covered during two growing seasons by 

 a foot of w^ater. Shaler described the habits of Ta.vodiiun dis- 

 tichum, the familiar cypress of our southern swamps. Where the 

 region is dry, the plant shows no peculiarity of root structure; but 



