[Sidenote: Fig. 7. _Nicolia Owenii_ (Carr.), from the Tertiary Strata of Egypt.]
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-Kurrân, in the inlet of Awaaba, on the eastern coast of Australia. In the inlet there is a formation of conglomerate and sandstone, with subordinate beds of lignite--the lignite forming the so-called Australian coal. Throughout the alluvial flat, stumps and 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 Casuarinæ 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 position. One was measured with a stem 6 feet high, a circumference 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 silicified 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 dicotyledonous trees (not coniferous), to which the names of Nicolia Ægyptiaca 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 ducts have transverse diaphragms. There are numerous medullary rays. The wood in their stems is converted into chalcedony. (Carruthers on Petrified Forest near Cairo. Geol. Mag., July 1870.)