I9I1.] STEVEXSOX— FORMATION OF COAL BEDS. 47 



Newberrv opposed the doctrine that spores of cryptogamous 

 plants are important constituents of coal. Sporangia and spores 

 are common enough in American coals but they are an inconsiderable 

 part of the whole. 



Dana,^* reasoning from chemical analyses, objected to Dawson's 

 suggestion that coal was derived largely from bark or material of 

 that nature. Though nearer coal in composition than is true wood, 

 bark resists alteration longer and is less easily converted into coal. 

 The occurrence of stumps and stems outside of the coal beds, " while 

 proof that the interior wood of the plants was loose in texture and 

 very easily decayed, is no evidence that those trees contributed only 

 their cortical portion to the beds of vegetable debris. Moreover, 

 the cortical part of Lepidodendrids (under which group the Sigil- 

 larids are included by the best authorities) and of Ferns also, is 

 made of the bases of the fallen leaves, and is not like ordinary bark 

 in constitution ; and Eqniscta: have nothing that even looks like bark. 

 This cortical part was the firmest part of the wood ; and for this 

 reason it could continue to stand after the interior had decayed away 

 — an event hardly possible in the case of a bark-covered conifer, how- 

 ever decomposable the wood might be. Further, trunks of conifers 

 are often found in the later geological formations, changed tlirough- 

 oiit the interior completely to Brown coal or lignite.'" He appears to 

 be convinced that the whole plant material contributed to formation 

 of the coal, which he regards as the product of marsh accumulation. 



Dawson'^' returned to the discussion in view of Huxley's asser- 

 tion that spores are an important constituent of the coal-forming 

 mass. Referring to his study of more than eighty coal beds in Nova 

 Scotia and Cape Breton, he asserts that the trunks of SigiUaria and 

 similar trees constitute the great part of the densest portion of the 

 coal and that cortical tissues, rather than wood, predominate. 

 Spores and spore cases, though often present abundantly, constitute 

 only an infinitesimal part of the great coal beds. Sporangites or 

 bodies resembling them are present in most coals, but they are acci- 



" J. D. Dana, '"Manual of Geology,"' 2d ed.. X'ew York, 1874, pp. .361, 

 362. 366. 



"J. W. Dawson. Amcr. Jauni. Sci., 1874. Supplement to 2d ed. of 

 " Acadian Geology," 1878, pp. 65. 



47 



