1913.] STEVENSON— FORMATION OF COAL BEDS. 149 



very often contain macroscopical masses of resins, which, in color, 

 are very similar to the material revealed by the microscope. 

 Pal?eobotanists have discovered in ferns certain organs closely 

 resembling those which, in modern ferns, secrete resins and there 

 appears to be good reason for supposing that Sigillarids yielded 

 much resinous material. The gums, resins and other substances, 

 originally soluble or rendered soluble by microorganisms, would be 

 deposited in tissues and crevices. The feature is familiar in recent 

 bogs and those of the Quaternary, where the fluidal ulmic and other 

 allied substances fill not only cavities in the bogs but also in the 

 underlying bed. 



The formation of the cannels and bogheads would seem to be 

 explained sufficiently by the earlier conception, which has the double 

 merit of simplicity and of accordance with conditions known to 

 exist. The minerals consist of vegetable muds with contribution 

 more or less important by plants and water animals. The great 

 abundance of spores and pollen grains is paralleled in modern times 

 by showers of pollen, the "sulphur showers'' in wide areas; fresh- 

 water algas abound in pools of actual swamps — possibly their exist- 

 ence in Coal Measures times is still problematical. Modern sapro- 

 pelic deposits bear, in many ways, very striking resemblance to can- 

 nels and bogheads, though certainly there is no evidence of a "bitu- 

 men " infiltration. But the hypothesis of extraneous origin of the 

 " bitumen " seems to be unnecessary, so that, to be accepted, it should 

 be supported by incontestable evidence. Lesquereeux^*® cites Zieg- 

 mann's analysis of an impure peat, which yielded 6.2 per cent, of 

 wax, 0.4 per cent, of resin, and 9 per cent, of " bitumen." It is 

 sufficiently well known that peat, subjected to destructive distilla- 

 tion, gives ample evidence of containing bituminous matter. The- 

 nius, cited by Davis, ^^^ has shown that air-dried peat yields 6.39 

 per cent, of petroleum, lubricating oil and paraffin wax, besides 40 

 per cent, of tar oil. The dried tar yields 54 per cent, of the same 

 substances and a notable quantity of ammonium sulphate. The 



"*L. Lesquereux, Sec. Geol. Surv. Penn., Rep. for 1885, p. 117. 

 "'C. A. Davis, "The Uses of Peat," U. S. Bur. of Alines, Bull. 16, 191 1, 

 p. 136. 



