144 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



They condensed bitumen energetically as did also the hard tissues of 

 plants, which give glance coal. The fleurs d'eau descended in sheets 

 with other accidental bodies, the speed of descent depending on the 

 stage of water; if the water were low, the fundamental jelly would 

 retard or prevent descent. Absolutely tranquil water was essential 

 and the precipitation of ulmic matters by calcareous waters was con- 

 stant. The " bitumen," absorbed by the various bodies, is regarded 

 by Bertrand as a substance intervening wholly formed and coming 

 from external sources. He suggests that it may have been in the 

 water, but, in any event, he could find no evidence to show that it 

 came from the decomposing plants. 



The resemblance of these bodies to algse was recognized by von 

 Giimbel who saw more than one type, as did also Fischer and Rust, 

 but they entertained enough doubt to prevent them from giving 

 generic and specific titles to the forms. Some later students have 

 felt compelled to dissent from Bertrand and Renault's conclusions 

 respecting the algae-like forms. Jeffrey^*^ subjected the whole series 

 of cannels and bogheads to microscopic analysis. By special treat- 

 ment he succeeded in reducing the minerals to such condition that 

 he could cut serial sections with the microtome ; and in this way he 

 made a great number of slides, giving opportunity for study not 

 possessed by his predecessors. Jeffrey's results confirmed Renault's 

 conclusion that the cannels are composed in great part of flattened 

 spores from vascular cryptogams, which are shown better in Amer- 

 ican than in European cannels. According to Jeffrey, the bogheads 

 of Kentucky, of Scotland and of Autun contain readily recognizable 

 spores — the forms termed algas by Bertrand and Renault being really 

 spores of vascular cryptogams — and a similar conclusion is reached 

 respecting the forms observed in the Kerosene shale. Jeffrey is 

 convinced that the well-preserved individual elements in these min- 

 erals are spores and he thinks that cannel and boghead are alike in 

 origin. The plates accompanying his memoir are elaborate. 



Thiessen's^*^ results have not been published and only a brief 



^*' E. C. Jeffrey, " On the Nature of Some Supposed Algal Coals," Proc. 

 Amer. Acad. Sci., Vol. XLVL, 1910, pp. 273-290. 



"^ R. Thiessen, "Plant Remains Composing Coal," Science, N. S., Vol. 

 XXXIIL, 1911, pp. 551, 552. 



