92 THE PRESERVATION OF PLANTS AS FOSSILS. [CH. IV] 



to imitate the natural processes of plant mineral isation\ By 

 soaking sections of wood for some time in different solutions, 

 and then exposing them to heat, the organic substance of the 

 cell walls has been replaced by a deposit of oxide of iron and 

 other substances. Fern leaves heated to redness between pieces 

 of shale have been reduced to a condition very similar to that of 

 fossil fronds. Pieces of wood left for centuries in disused mines 

 have been found in a state closely resembling lignite'''. Attempts 

 have also been made to reproduce the conditions under which 

 vegetable tissues were converted into coal, but as yet these 

 have not yielded results of much scientific value. The Geysers 

 of Yellowstone Park have thrown some light on the manner in 

 which wood may be petrified by the percolation of siliceous solu- 

 tions ; and it has been suggested that the silicification of plants 

 may have been effected by the waters of hot springs holding 

 silica in solution. Examples of wood in process of petrifaction 

 in the Geyser district of North America have been recorded by 

 Kuntze^, and discussed by Schweinfurth^ Solms-Laubach^ 

 and others ^ The latter expresses the opinion that by a long 

 continuance of such action as may now be observed in the 

 neighbourhood of hot springs, the organic substance of wood 

 might be replaced by siliceous material. The exact manner of 

 replacement needs more thorough investigation. Kuntze de- 

 scribes the appearance of forest trees which have been reached 

 by the waters of neighbouring Geysers. The siliceous solution 

 rises in the wood by capillarity ; the leaves, branches and bark 

 are gradually lost, and the outer tissues of the wood become 

 hardened and petrified as the result of evaporation from the 

 exposed surface of th^ stem. The products of decay going on 

 in the plant tissues must be taken into account, and the double 

 decomposition which might result. There is no apparent reason 

 why experiments undertaken with pieces of recent wood ex- 

 posed to permeation by various calcareous and siliceous solutions 

 under different conditions should not furnish useful results. 



1 Goppert (36), etc. ^ Hirschwald (73). ^ Kuntze (80) p. 8. 



^ Schweinfurth (82). ^ Solms-Laubach (91), p. 29. 



6 Goppert (57). Some of the large silicified trees mentioned by Goppert may 

 be seen in the Breslau Botanic gardens. 



