150 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



10. The Flora. — The Cretaceous coals are usually so far ad- 

 vanced in conversion as to give little information respecting the 

 plants by which they were formed. Knowledge of the flora of the 

 period is derived from fragmentary material found in the rocks ; 

 that has been transported, it represents mostly the upland vegeta- 

 tion and tells nothing about the swamp plants. In the United States 

 and Canada, the coals are often rich in resins, indicating that coni- 

 fers entered largely into their composition ; such wood as has been 

 recognized seems to confirm this conclusion. Cycads were abundant 

 locally during the Kootenai but conifers and dicotyledons were pre- 

 dominant during the Upper Cretaceous, when ferns and lycopods 

 appear to have been subordinate. Memoirs on European coals, 

 consulted by the writer, usually contain little information upon the 

 subject. Wood, fully recognizable, is present in the Upper Cre- 

 taceous coal of the Loew^enberg region, but in the Griinbach coal, no 

 structure is shown, though the stems and branches retain their form. 

 The Wealden of Hannover contains abundance of conifers, cycads. 

 lycopods and ferns ; the plant remains in coal must be distinct there. 

 Dunker thinks that the " black coal " of that region was derived from 

 lycopods and ferns, because they are the only forms found in it ; the 

 lignitic brown coal is largely of conifer origin, as the stems occur- 

 ring in it resemble Pinits. 



11. CJicmical Relations. — Discussion of the chemical relations 

 of Cretaceous coals must be deferred until the older coals have been 

 studied ; but it may be well to call attention to some matters. 



Like the Tertiary coals and some peats, these coals are resinous 

 in many districts. Cannel is present at several horizons, with all 

 features wdiich mark the sapropels or Lebertorfs of later times. The 

 carbon content is higher than that of Tertiary coals, but progressive 

 enrichment with increasing age is less marked. In the Fox Hills 

 the extremes of carbon are 73 and 84; in the Pierre, 71 and 84; in 

 the Benton, yy and 83, and in the Kootenai, 75 and 85. No note 

 has been taken here of metamorphosed coals ; anthracite is present 

 at several horizons. No ultimate analyses of the Laramie coal are 

 available and there are very few of the Kootenai. The variations 

 are small compared with those in the Tertiary. In the Cretaceous 

 as in the Tertiary, not all accumulations of vegetable materials had 



