10 PAL^ONTOLOGICAL BOTANY. 



woods, often preserves all the tissues equally, at other times 

 the soft tissues are altered or destroyed ; the cellular tissue 

 being replaced by amorphous chalcedony, while the ligneous 

 and vascular tissues alone are petrified, so as to preserve their 

 forms. In some cases the reverse takes place as to these tissues; 

 the fibrous portions disappear, leaving cavities, while the cells 

 are silicified. Sometimes we find the parts regularly silicified 

 at one place, so as to retain the structure, while at another 

 an amorphous mass of silica is found. In such cases there 

 appear, as it were, distinct silicified woody bundles in the 

 midst of an amorphous mass. The appearance depends, how- 

 ever, merely on irregular silicification or partial petrifaction. 

 Infiltrated fossil woods, by means of chemical tests, are shown 

 to possess portions of vegetable tissues cemented into a mass 

 by silica. In some cases we find the vessels and cells sepa- 

 rately silicified, without being crushed into a compact mass. 

 In these cases, the intercellular substance not being silicified, 

 the mass breaks down easily ; whereas, when complete silicifi- 

 cation takes place, the mass is not friable. Coniferous wood 

 is often friable, from silicified portions being still separated 

 from each other by vegetable tissue more or less entire. 

 During silicification, or subsequent to it, it frequently hap- 

 pens that the plant has been compressed, broken, and de- 

 formed, and that fissures have been formed which have been 

 subsequently filled with crystallised or amorphous silica. 



Silicified stems of trees have been observed in various 

 parts of the world, with their structure well preserved, so that 

 their Endogenous and Exogenous character could be easily 

 determined. The Rev. W. B. Clarke notices the occurrence 

 of a fossil pine-forest at Kurrur-Kurran, in the inlet of 

 Awaaba, on the eastern coast of Australia. In the inlet there 

 is a formation of conglomerate and sandstone, with sub- 

 ordinate beds of lignite — the lignite forming the so-called 

 Australian coal. Throughout the alluvial flat, stumps and 



