82 



THE PRESERVATION OF PLANTS AS FOSSILS. 



[CH. 



specimen show scattered circular patches (fig. 14 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 [Araucarioxylon Withami (L. 

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

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



«?*■ 



Fig. 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. 2^. Remains of the pith 



tissue. 



Primary xylem. 



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 



