38 STEVENSON— FORAIATION OF COAL BEDS. [April 21. 



lions observed in the numerous coal beds, he presents these con- 

 clusions : 



( I ) The occurrence of Stigmaria under nearly every bed of coal 

 proves accumulation /;/ situ; the sediments between the beds prove 

 transport of mud and other materials, the conditions being those 

 observed in swampy deltas. (2) True coal consists mostly of bark 

 of Sigillarid and other trees, leaves of ferns and Cordiates with 

 other debris, fragments of mineral charcoal, all grown and accu- 

 mulated where they are found. (3) Microscopic structure and 

 chemical composition of cannel and earthy bitumen as well as of the 

 more highly bituminous and carbonaceous shales prove that they 

 were fine vegetable mud as in the ponds and lakes of modern swamps. 

 (4) A few undcrclays consist of this vegetable mud, but most of 

 them are bleached by drainage. They contain not sulphide but car- 

 bonate of iron; rain, not seawater, percolated through them. (5) 

 Most of the erect and prostrate trees had become hollow shells of 

 bark before final cmljedding and their wood had been broken into 

 cubical pieces of mineral charcoal ; land snails, galley worms and 

 reptiles were caught in them. There is much mineral charcoal on 

 surfaces in all the larger coal beds. (6) Sigillaria roots have much 

 resemblance to rhizomas of certain aquatic plants, but structurally 

 are identical with cycad roots, which the stems resemble. SigillaricB 

 grew on soils supporting conifers, Lcpidodciidra, Cordaitcs and 

 ferns, which could not grow in water. There is remarkable absence 

 of aquatic vegetation. (7) The occurrence of marine or brackish 

 water forms is no evidence of sub-aqueous formation. The same 

 condition is observed in the case of submerged forests. 



The channels, sand or gravel ridges, ine(jualities of floor observed 

 in coal beds are familiar features of modern swamps. The lamina- 

 tion of coal is not aqueous lamination ; it is the superposition of suc- 

 cessive generations of more or less decayed trunks and beds of 

 leaves. It is very dififerent from the lamination observed in cannels 

 and in the carbonaceous shales. 



The doctrine that coal is composed of the debris of land plants, 

 though maintained by nearly all students, did not pass unchallenged. 

 As far back as 181 5, Parrott suggested that seaweeds had contrib- 



38 



