3 



INTRODUCTION. 



cumstances couched in too general terms : ' The silicified trees are therefore 

 never produced under water, but in situ above the surface of the ground 

 by the constant supply of comparatively small quantities of siliceous water 

 from geysers or hot springs ; the water rises in the wood by capillary 

 attraction and evaporates gradually in the open air.' Herr Kuntze has 

 been kind enough to supply me with a small piece of fir-wood taken from 

 one of the erect tree-stumps in Firehole Basin, which is of a spongy fibrous 

 texture, and of a brown colour inside but whitish on the outside, as described 

 above. From all the white parts I obtained, after destruction of the 

 organic substance by means of sulphuric acid, fusiform siliceous spiculae, 

 which looked somewhat corroded on the sides, and might stand for the casts 

 of the cells in which they originated. It seems very natural to explain in 

 this way with Kuntze the origin of other similar fossil woods mentioned 

 above, and there is still a possibility that with long continuance of the 

 process, resulting in more complete disappearance of the organic substance 

 of the membranes and the cementing together of the spiculae by the 

 solution of silicic acid penetrating between them, even dense compact 

 petrifaction may be produced. Renault l inclines to the view that the 

 majority of compact non-porous fir-woods originated in this way. I may 

 add that sections of some of these woods, that of Nicolia aegyptiaca, for 

 example, from the petrified forest at Cairo, lying before me, do in fact 

 favour this view, which is also warmly supported by Schweinfurth 2 . The 

 appearance is as if sharply defined cones answering to the cells of the wood 

 had been simply imbedded, fixed in a homogeneous matrix. All things 

 considered, it is very desirable that further investigation should be devoted 

 to this subject, in which many points still require elucidation. 



Lastly, there is a point of importance to be considered in connection with 

 vegetable petrifactions. The process of petrifaction may begin at once while 

 the stem is standing, or immediately after it has been laid in its place of 

 deposit, but it may also be deferred to a much later time when the organic 

 remains are already converted into coal or are in process of conversion. 

 Unger 3 quotes as an instance of this the Miocene beds of lignite at Sagor in 

 Carinthia, in which the seam is silicified in places to such an extent that the 

 work of mining has to be modified accordingly. Isolated pieces of silicified 

 wood are everywhere of frequent occurrence in beds of lignite. 



Local processes of petrifaction, though much more scattered and in- 

 frequent, are also observed in seams of coal ; these appear generally to 

 have taken place at a time when the seam had not yet attained its full 

 development. The agent of petrifaction is either siHcic acid or some 

 carbonate. The vegetable remains which form the seam are usually mixed 



Renault (2), Introd. a Schweinfurth (1). 3 Unger (6). 



