STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 45 



from Doliewen. This had convinced Friih that the micrococcus- 

 forms are not all Chroococcace?e. He is certain, at all events, that 

 Lebertorf is not genetically an algse peat ; the algse are only acces- 

 sory; pollen plays the chief role. • 



The elaborate microscopical examination of oil shales by Bertrand 

 and Renault after 1890 led them to look upon those shales as accumu- 

 lations of algre and remains of other types carried down during 

 precipitation of organic salts — an explanation very similar to that 

 suggested by H. v. Post. Tliese studies recalled similar studies of 

 coal by Reinsch and led to farther study of Lebertorf. Potonie'^*^ 

 made examinations in many localities, which he discussed at various 

 times, publishing his final conclusions in 1910. The Lebertorf of 

 Caspary, Faulschamm and plankton deposit of authors, is termed 

 sapropellite by him. It contains diatoms, Pcdiastniiii and other 

 forms of alg^e with pollen of Pinus, Coryliis, Alnus and Bctitla along 

 with remains of various aquatic animals. It accumulates rapidly in 

 enclosed basins and it has rendered some German lakes so shallow 

 that they are no longer navigable. Jefi^rey'" has observed that the 

 bottom of lakes and ponds becomes covered with vegetable matter 

 swept in by breezes or washed in by rains. This is finer in the deeper, 

 less disturbed portions, but coarser in the shallower parts. In one of 

 his figures, showing the finer type, one finds excrement of fish, snails 

 or amphibia, mingled with pollen of conifers. In the other, showing 

 the coarser material, there are merely remains of roots, leaves and 

 other vegetable " flotsam and jetsam." It is noteworthy that he has 

 found no trace of algse in the lacustrine muck examined by him. 

 Pollen grains and spores are the most important constituents. 



The composition of Lebertorf is variable, certain constituents 

 being more abundant at some localities than at others ; but of all the 

 constituents, pollen appears to be the most important ; other remains 

 are to be regarded almost as accessory, though always present. 



Lebertorf cannot be recognized at all localities. Not infrequently 

 it is absent in the lake deposits of north Germany as also in many 

 of tho'se in Sweden and Switzerland. Undoubtedly, the plankton 



36 H. Potonie, " Enstehung," etc., pp. 19-22. 



^'^ E. C. Jeffrey, " On the Composition and Qualities of Coal," Econ. 

 Geol, Vol. IX., 1914, p. 72iZ, Figs. 151, 152. 



