18 GEOLOGICAL MEMOIRS. 



uniting in compounds with carbonic acid and carburetted hydrogen, 

 escape when the air has access. Covering up the plants prevents the 

 latter process, or rather only checks it ; for, as experience teaches, 

 such combinations are developed in both brown and stone-coal pits 

 when they are opened, — in the former particularly as carbonic acid 

 gas, in the latter as carburetted hydrogen combinations, — and thus 

 prove that a change is continually proceeding, which, when it had de- 

 prived the coal of all its hydrogen, would convert it at last into an- 

 thracite. This separation of elements, which gradually converted the 

 vegetable mass into coal, took place with the cooperation of moisture 

 or in the humid way, as the preservation of all the plants found in 

 the coal-formation proves. Such processes, as I have observed, are 

 occurring even at the present day before our eyes in nature, and, as I 

 proved by experiments, can be designedly produced by means of si- 

 milar conditions ; and this indeed has respect not only to the forma- 

 tion of the brown coals, but also of the common black coal. 



The condition of the coal strata broken through by eruptive rocks, 

 — their beds of slate-clay and sandstone burned red by this catastro- 

 phe, with the coal partially converted into coke, even the gradual in- 

 crease or decrease of this appearance, with the greater or less proximity 

 to the eruptive mass, — may also fuiTiish us with a proof of the state- 

 ment above, since it exhibits the effects of the action of heat {the dry 

 way) in such a sharp and decisive manner. 



VII. The influence of pressure completed the process of which the 

 commencement is described in the previous section. 



The beds of coal already in course of formation were buried below 

 the fragments of ancient mountains, broken up during the eruption 

 of the older massive rocks, or by volcanic showers, violent spring- 

 tides with their detrital deposits, streams of mud poured out from 

 volcanos during these convulsions, or river-sand and lacustrine de- 

 posits, which also enveloped the similar vegetation that from time to 

 time appeared in particular localities, and is now met with in the 

 slate-clays and sandstones. At the time of these deposits the coal- 

 beds had already acquired a considerable degree of compactness. This 

 is proved by the impressions formed on the slate-clays and sandstones 

 above them by plants found on the surface of the coal-beds. These 

 were first observed in Lower Silesia by my friend Beiner and myself, 

 and I subsequently saw them still more extensively in Upper Silesia 

 in some of the open workings {Taghauten). Although no one would 

 maintain that this deposition took place everywhere with equal tran- 

 quillity, yet my observations in many localities on the distribution of 

 fossil plants, their division into groups, or the social and isolated oc- 

 currence of certain species, the absence of one kind and its replace- 

 ment by another species of the same genus on the roof of one and the 

 same bed of coal, and finally, above all, the wonderful preservation of 

 fossil plants, which sometimes, as in particular points in Upper Silesia 

 and Zwickau, appear like newly-dried, slightly-browned leaves, prove 

 undeniably that they have been buried in the beds of clay and sand 

 either in their original place of growth or at least not far from it. 

 The diverse physical conditions and the distinct vegetation of the 



