82 



THE PRESERVATION OF PLANTS AS FOSSILS. 



[CH. 



specimen show scattered circular patches (fig. 14i A) in the 

 mineralised wood in which the tracheids are very clearly pre- 

 served ; while in the other portion the preservation is much less 

 perfect. The patch of tissue in fig. 14 A shows a portion of 

 the wood of the Craigleith tree [Araucarioscylon Withami (L. 

 and H.)] in which the mineral matter, consisting of dolomite 

 with a little silica here and there, has crystallised in such a 



,? - '/> 



*«i%. 



Pig. 15. Transverse section of the central cylinder of a Carboniferous Lepido- 

 dendroid stem in the collection of Mr Kidston. From Dalmeny, Scotland, 

 s. Silica filling up the central portion of the pith. p. Eemaius of the pith 

 tissue, x^. Primary xylem. x^. Secondary xylem. c. Innermost cortex. 



manner as to produce what is practically a cone-in-cone 

 structure on a small scale, which has partially obliterated the 



