470 J^oflces of Memoirs — E. Wethered on Forination of Coal. 



underclays represent the roots of the coal-forming vegetation, we 

 slionld expect to find the fructifications immediately over the coal, 

 which is not the case ; with the exception of Cordaites, remains of 

 fossil plants are not found for the first two feet or so over the coal. 



After a careful investigation underground of the conditions under 

 which coal was formed, the author has arrived at the following con- 

 clusions: — On the land grew the vegetation of the period, represented 

 by Zepidodendra, Sigillaria, Calamites, etc. As the land sank and 

 the waters encroached, the land vegetation gradually disappeared, 

 but the roots remained in many cases, and those which offered the 

 greatest resistance to decay are the ones preserved in a fossil state — 

 hence the occurrence of Stigmaria. As the waters advanced, the 

 ground would become swampy, and then we might expect to see 

 spring up reeds, mosses, and other vegetation suitable to the changed 

 condition ; it is to vegetation of this kind that the author ascribes 

 the formation of coal. 



Eeference was then made to the Presidential Address of Professor 

 Eamsay to the British Association in 1880, in which the recurrence 

 of the same kind of incident through geological time was advocated. 

 The author then asked, why the coal formations of the Carboniferous 

 period should be an exception, seeing that the modern lignites and 

 deposits of peat were instances of coal in the process of formation. 

 It was then pointed out that these deposits were not composed of 

 large trees, but of a lower order of growth. 



Coming to the varieties of coal, and the change which sometimes 

 takes place in this respect in one and the same seam, it was shown 

 that the difference between bituminous and anthracite coal was, that 

 the latter contained a greater proportion of carbon and a less amount 

 of volatile matter than the former. It was then contended that if 

 the decomposition of the coal-forming vegetation took place without 

 being affected, to any extent, by minerals capable of oxidizing the 

 carbon, that a coal would be formed having a large proportion of 

 carbon with a less proportion of volatile matter than is found in 

 bituminous coals. The author explained this by briefly reviewing 

 the process by which vegetable matter has been converted into coal. 

 It chiefly depended upon the amount of oxygen which could unite 

 with the carbon for carbonic acid, and the amount of hydrogen which 

 could unite with the carbon to form marsh gas. By this process 

 oxygen and hydrogen would pass off in greater proportion than the 

 carbon, thus increasing the proportion of the latter to the whole. If, 

 however, the submerging waters placed in contact with the vegetable 

 mass substances capable of supplying oxygen to the carbon, then 

 there would be a decrease in the proportion of the latter, and what 

 the author termed the 'fixed oxygen and hydrogen ' would increase 

 in proportion to the whole and give rise to a coal of a bituminous 

 nature. 



With a view of ascertaining whether the chemical composition of 

 the beds overlying a seam of coal which has changed from bituminous 

 to anthracite also changed, the Welsh 'nine feet' seam was selected, 

 which near Cardiff is semi-bituminous and at Aberdare becomes 



