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



many readers of Bertrand's memoirs. The invading bitumen must 

 have possessed extreme fluidity, as it was injected into all parts of 

 the vegetable debris, passing even through the walls of cellules; 

 but that fluidity would have led to complete penetration of the 

 sandstones and shales in which one finds the often widely isolated 

 coaled plants; but no evidence of that penetration is seen. He 

 objects also that if the penetration had been made into tissues, the 

 coal should have the appearance of a compact resinous mass; but 

 the coaled wood is porous and he found no "bitumen" in cells and 

 vessels. 



The term "bitumen," as employed by Bertrand, is extremely 

 vague and its actual signification cannot be gathered from any of 

 his writings. A reference to the La Brea (Trinidad) conditions 

 suggests that a petroleum is the supposed source. This area was 

 studied by Cunningham-Craig,^*' who states that the Rio Blanco 

 sandstone has so much petroleum that, though tide-washed, it has 

 15 to 18 per cent, of sticky oil or soft pitch on the surface, and it 

 constantly exudes similar material into the Pitch Lake. The exist- 

 ence of such asphaltic matter would be recognizable in the rock after 

 any period, no matter how long — one finds asphalts in Carboni- 

 ferous limestones and sandstones. The glance coal in sandstones is 

 caking, rich in bitumen. The objection, however, is not insuper- 

 able. A light-colored oil with paraffin base might leave no notable 

 trace in the sandstone. At the same time, one must bear in mind 

 that paraffins do not change, and that the great supply is from 

 Palaeozoic rocks. If they penetrated the rocks and the tissues, it 

 is certainly strange that certain solvents extract so little from coal or 

 cannel or boghead. Destructive distillation, under similar condi- 

 tions, obtains rather abundantly from coals some substances which 

 are almost absent from petroleums. 



But one cannot resist the query. Why go outside of the decom- 

 posing mass for the source of "bitumen"? If a source can be 

 found in that mass, there seems to be no good reason for searching 

 after recondite sources. Coals, even those of Carboniferous age, 



"^ E. H. Cunningham-Craig, " Preliminary Report on Guapo and La Brea 

 District," Council Paper, No. 30, 1906, pp. 3, 4. 



