IV] 



PETRIFIED WOOD. 



81 



beech from a Roman aqueduct at Eibsen in Lippe Bucheburg, 

 he says : — 



" The wood is, for the most part, in the state of very old dry wood, but 

 there are several insulated portions, in which the place of the wood has 

 been taken by carbonate of lime. These portions, as seen on the surface 

 of the horizontal section, are irregularly circular, varying in size, but 

 generally a little less or more than ^ of an inch in diameter, and they 

 run through the whole thickness of the specimen in separate, perpendicular 

 columns. The vessels of the wood are distinctly visible in the carbonate 

 of lime, and are more perfect in their form and size in those portions of 

 the specimen than in that which remains unchanged i." 



This partial petrifaction of the structure in patches is 

 often met with in fossil stems, and may be seriously misleading 

 to those unfamiliar with the appearance presented by the 

 crystallisation of silica from scattered centres in a mass of 

 vegetable tissue. A good example of this is afforded by the 

 gigantic stems discovered in 1829 in the Craigleith Quarry near 

 Edinburgh^ Of those two large stems found in the Sandstone 

 rock, the longest, originally 11 meters long and 3"3 — 3 9 meters 

 in girth, is now set up in the grounds of the British Museum, 

 and a large polished section (1 m. x 87 cm.) is exhibited in the 



A B 



Fio. 14. 



A. Araucarioxylon Withavii (L. and H.). Eadiating lines of crystallisation in 

 secondary wood, as seen in transverse section. 



B. Lepidodendron sp. Concentric lines of crystallisation, and scalariform 

 tracheids, as seen in longitudinal section. 



Fossil-plant Gallery. The other stem is in the Botanic Garden, 



Edinburgh. Transverse sections of the wood of the London 



1 Stokes (40) p. 207. ^ Witham (31), Christison (76). 



6 



