22 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



ficoidcs with its fibrous processes. The roof contrasts with the 

 underclay and is, normally, a laminated shale due to more or less 

 rapid current and it contains va^st numbers of plant impressions. 



When the roof is sandstone there is evidence of tempestuous cur- 

 rents and the vegetable fragments are trunks and stems of large 

 plants. Occasionally limestone forms either roof or sole of the coal 

 bed but there is usually a very thin layer of calcareous shale parting 

 them. 



No hypothesis, thus far presented seemed satisfactory to Rogers, 

 and he presented his own to account for origin of the Coal Measures. 



He imagined extensive flats bordering a continent, the shore of 

 ocean or bays, beyond which was open sea. The whole period of 

 the Coal Measures was characterized by a general slow subsidence 

 of the coasts, interrupted by pauses and gradual upward movements 

 of less frequency and duration, and these merely statical conditions 

 alternated with great paroxysmal displacements of the land. During 

 gentle depression, the coast was fringed by marshes while arborescent 

 plants were on the land side. The meadows would give pulpy peat; 

 leaves blown in or moved by higher tide would rest on the peat ; some 

 would be buried and become pulpy, or, in some cases, by rapid re- 

 moval of volatile constituents would remain as mineral charcoal. An 

 earthquake comes. Water is drained from the swamps and their 

 tributaries ; muddy water draws from swamp and swampy forests 

 leaves -and the rest to distribute them with the mud over the bog. 

 This is the laminated shale. The sea returns, rolls over the swamp 

 to the dry land ; withdrawing, it brings uprooted trees, and washed 

 ofif soil, strewing the land stuiT in a coarse promiscuous stratum. 

 Repeated waves would add to the mass. The disturbance ends; 

 coarse materials sink, then the less coarse and last of all the finest 

 sediment, light vegetable matter and the buoyant stems of Stigmaria, 

 would sink together. A new marsh would be made and once more 

 the savannahs would be clad with vegetation. This he terms the 

 paroxysmal theory. 



Petzholdt"- found two questions involved in the problem; were 

 coal beds formed during a brief period and were they formed in situ 



^'A. Pclzholdt, "Geologic," Zweite Auilage, Leipzig, 1S45, pp. 413-417. 



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