432 SCIENCE PROGRESS. 



of considerable interest ; these are rounded pieces of coal oc- 

 casionally met with in seams of coal of a somewhat different 

 physical nature to the included balls. Logan long ago 

 mentioned their occurrence in South Wales, and Renault, 

 Fremy and others have since described them at some 

 length, and discussed their probable manner of formation in 

 the case of the French Coal- Measures. These balls are 

 frequently more porous than the coal in which they occur ; 

 they are looked upon as water-worn fragments of older 

 carbonaceous strata. Renault and others make use of 

 the coal balls as an argument in favour of the rapid car- 

 bonisation of vegetable deposits ; they believe that certain 

 beds of plant material in the Commentry basin were con- 

 verted into a more or less porous form of coal, and suffered 

 disintegration prior to the complete deposition of other 

 seams in the same area. 



Whilst some geologists have preferred to regard coal as 

 an advanced stage in the gradual compression and chemical 

 alteration of peat mosses, others have held fast to the idea 

 that each seam of coal marks the site of a thick mass of 

 vegetable accumulation, derived from a dense and long-con- 

 tinued forest growth on a gradually subsiding area. " The 

 same area was alternately covered with vast forests, such 

 as we see in the deltas of great rivers in warm climates, 

 which are liable to be submerged beneath fresh or salt 

 water should the land sink vertically a few feet." 1 



Geikie, in the recent edition of his text-book, briefly de- 

 scribes this autochthonous method of coal formation, but goes 

 on to devote a few lines to Fayol's work in the Commentry 

 coalfield of France, and admits the strong case which this 

 experienced geologist has founded on his detailed re- 

 searches. Geikie concludes by expressing the opinion that 

 " it would thus appear that no one hypothesis is universally 

 applicable for the explanation of the origin of coal, but that 

 growth on the spot and transport from neighbouring land 

 have both, in different regions, contemporaneously and at 



1 Lyell (i), p. 388. (Good figures of " spore coal " sections are given 

 on p. 405.) 



