42 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



to the mineral floor, it would pass through beds of the several stages, 

 each of which would be crossed in following the surface from the 

 Hochmoor to the water's edge. 



But one must always bear in mind that the order as given is not 

 absolute ; it is merely that observed where the filling of a basin has 

 been continuous and undisturbed ; any .one or most of the stages may 

 be omitted and any stage may be repeated. Local conditions control 

 the succession. That in Michigan, as ascertained by Davis, is, ascend- 

 ing, (i) A deposit formed by Chara and floating algse; (2) in the 

 shallower water, Potamogeton followed by water-lilies; (3) next 

 behind is the floating mat of sedges extending to a considerable dis- 

 tance from the shore; material from the under side of this mat accu- 

 mulates near the shore and (4) shrubs and Sphaginiiii appear; (5) 

 tamarack and spruce advance with ferns. 



These stages are distinct around the open water and the trees 

 are all rooted in the peat, which continues to accumulate while the 

 trees are growing. Sphagnum is seen first after the surface rises 

 to 2 inches above the water-level. 



This general succession is that observed in peat deposits formed 

 within gradually shallowing water-basins ; it applies only locally to 

 the great deposits formed on extensive plains. 



The Lebertorf or Sapropel Stage. — Klaproth"'^ appears to be the 

 first describer of the material known in later time as Lebertorf. 

 In 1807, he reported the chemical composition of a new combustible 

 " fossil," which came from near Bartenstein in East Prussia. The 

 detailed description of the substance leaves no room for doubt as to 

 its relations. No later notice has been seen by the writer prior to 

 those by Steenstrup and von Post.^^ The former recognized a de- 

 posit of amorphous material which rests on tlie underclay of bogs, 

 while the latter described the Dytorf, which usually underlies the 

 peat. The substance was rediscovered by Caspary^- in 1870. He 



30 M. H. Klaproth, " Beitrage zur chemischen Kenntniss der Mineral- 

 korper," Vol. IV., 1807, pp. 378, 379. 



31 Streenstrup, summarized by Morlot, trans, in Ann. Rep. Sniifhson. Inst._ 

 1861, pp. 304 ff. ; H. von Post in Swedish Academy, 1861. 



32 R. Caspary, " Lebertorf von Purpesseln," Schrift. k. phys.-okon. Ges 

 Konigsherg, liter. Jahrg. 1870, Sitz., pp. 22, 23. 



