748 TRANSACTIONS OF SECTION K. 



of the coal-balls; in twenty yards a 'pocket' may be worked through. The 

 evidence which could be collected under the difficult conditions of underground 

 work went against rather than in support of the view that they had been brouo-ht 

 by streams at the time of the deposition of the coal. 



Most of this work was done in collaboration with Mr. James Lomax and 

 Mr. D. M. S. Watson, though our views do not coincide in all cases. 



4. On the Origin of Coal. By Professor H. Potoni^. 



We have three kinds of coal : firstly, the bright coal ; secondly, the dull coal ; 

 and, thirdly, the strata coal, which is composed of layers of bright and of dull 

 coal. Between these different coals we have all transition stages. I set aside 

 those combustible biolithes which are pyromonimites, such as amber.^ 



If we regard the recent combustible biolithes which have certain characteris- 

 tics of coal, we have also three classes : first, the peat, which is also bright, 

 when it is thoroughly ripe, as the ' dopplerit'; secondly, the sapropel and sapro- 

 koU ; and, thirdly, the strata peat, which is a mineral composed of layers of peat 

 and of saprokoll. 



If we wish to understand the genesis of the fossil minerals I have named, we 

 must compare them with the genesis of the recent minerals. 



The sapropel is formed from the excrements and bodies of completely aquatic 

 animals and plants which have lived in stagnant water, and therefore, because 

 the water is stagnant, do not decay completely. Sapropel is a slime, or mud. 

 This sapropel becomes saprokoll when it is sub-fossilised, and is then of a gela- 

 tinous consistency. Even if the saprokoll is of Tertiary age ( = dysodil) it can still 

 be gelatinous. When it is of older geological formations it is very hard — exactly 

 like sapropel or saprokoll which has been dried in the air. In the coal 

 measures of the Carboniferous formation this is represented by the cannel coal, 

 which is a fossil sapropel. 



Genuine coal is fossil peat. If we look at it under the microscope it has the 

 same appearance as ripe peat, as Fr. Link, of Berlin, demonstrated in 1838. All 

 other facts also show that the genesis of peat and genuine coal is identical. Of 

 these facts I will mention the following : — 



Very often we have under the peat-seam soils with roots, rootlets, and 

 rhizomes, especially those of the reed-formation (Arundo Phragmites and other 

 species). The same is often the case under the layers of coal from cainozoic and 

 mesozoic formations, while under the coal seams of the Carboniferous formation 

 we have other plants, which form these soils : I mean the well-known ' under- 

 clays ' with stigmaria of British miners. Often, too, we see the trunks of trees 

 still arranged as if it were a forest — and it was once a forest. I cite as examples 

 the trunks at Whiteinch, near Glasgow, and at Osnabriick. In the peats it is a 

 common fact that there are forests of tree-trunks. 



The same characteristics which we see in the construction of the real bog 

 plants are displayed also by the plants of coal measures, such as the growing in 

 stages. 



The strata peat comes from places where the peat is periodically under water. 

 This produces sapropel, which again is covered with peat when the water dis- 

 appears. The coal which corresponds to the strata peat is very common. 



The chemistry of the bright coal on the one side and of the dull coal on the other 

 is very different, in the same way as the corresponding peats. The dull coal is 

 the gas coal, and the sapropelits gives also much more gas than the genuine peat. 



It will be interesting to the English, especially in the neighbourhood of 

 Whitby, to hear that the wood transformed into a sapropelit — and to the sapro- 

 pelits belong the bituminous limestones and clays — becomes jet,- which demon- 



' See Potoni^, Klagsification und Terminoloyie der recenten brennharen Biolithe, 

 Berlin, 1906. 



' See Gothan in iholNaturmissenschaftliche Wochenschrift, Jena, 1905. 



