MODE OF PRESERVATION OF FOSSIL PLANTS. 



11 



stools of fossilised trees are seen standing out of the ground, 

 and one can form no better notion of their aspect than by 

 imagining what the appearance of the existing living forest of 

 Eucalypti and Casuarinas would be if the trees were all cut 

 down to a certain level. In a lake in the vicinity there are 

 also some fossilised stumps of trees, standing vertically. In 

 Derwent Valley, Van Diemen's Land, fossil silicified trees, in 

 connection with trap rocks, have been found in an erect posi- 

 tion. One was measured with a stem 6 feet high, a circum- 

 ference at the base of 7 feet 3 inches, and a diameter at the 

 top of 15 inches. The stems are Coniferous, resembling 

 Araucaria. The outer portion of the stem is of a rich brown 

 glossy agate, while the interior is of a snowy whiteness. One 

 hundred concentric rings have been counted. The tissue falls 

 into a powdery mass. Silica is found in the inside of the 

 tubes, and their substance is also silicified. The erect silici- 

 cificd stems of coniferous trees exist in their natural positions 

 in the ^^ dirt-bed," an old surface soil in the sandstone strata 

 of the Purbeck series in the Isle of Portland, Dorsetshire. 

 In the petrified forests near Cairo silicified stems have been 

 examined by Brown, 

 Unger, and Carruthers. 

 They belong to dicoty- 

 ledonous trees (not 

 coniferous), to which 

 the names of Nicolia 

 iEgyptiaca and Nicolia 

 Owenii (Fig. 7) have 

 been given. The wood 

 consists of a slender 

 prosenchyma, abundantly penetrated by large ducts. The 

 walls of the ducts are marked by small, regularly arranged, 

 oval, and somewhat compressed hexagonal reticulations. The 

 Fig. 7. Nicolia Owenii (Carr.), from the Tertiary Strata of Egypt. 



Fig. 7. 



