5 



50. FRAGMENT OF SiLlCIFIED WOOD 



The structure of the sections is precisely similar to that of similar 

 sections of the fragment of wood broken directly from one of the 

 silicified stumps. 



2. As regards its chemical constitution, the wood has been com- 

 pletely fossilized, and the specimen consists essentially of silica. It 

 may be noticed in this connection that the specimen, in spite of its 

 complete mineralization, is remarkably light. A portion yielded to 

 chemical analysis as follows : 



Loss on ignition (Water and Organic Matter) ........ 6 24 



Silica 85.26 



Alumina 5.35 



Lime 6 . '79 



Magnesia.) .._,^. ,._,^^ , .Traces. 



iron ) 



103.64 



3. The microscopical and chemical examination of the specimen 

 place beyond a doubt its being truly of the nature of silicified wood, 

 and it only remains to consider its very remarkable form. 



The specimen has the form of an irregular rhombohedron, about six 

 inches in greatest length by three inches in greatest width ; and we 

 may successively consider its internal, external, superior and inferior 

 surfaces, holding it in such a position that the fibres of the wood have 

 a vertical direction. The internal and external faces of the fragment 

 present little of importance. Both, of course, are parallel with the 

 fibres of the wood, and the only means of determining with certainty 

 which is internal and which external, is to be found in the very 

 slight, indeed hardly noticeable, curvature of the woody layers. 

 Judging from these, the side towards which the convexity of the 

 layers is turned, and which is therefore external, is much the smaller, 

 owing to the fact that the superior and inferior faces of the fragment 

 are directed away from one another. There are no signs of the exist- 

 ence of the bark upon this face. The internal face is much more 

 extensive than the external (for the reason noticed above), and is 

 considerably discoloured and blackened, probably because the frag- 

 ment must have rested with this side in contact with the ground. 



The upper and lower surfaces of the fragment are both directed 

 across the fibres of the wood, and, as before intimated, are directed 

 away from one another. The upper surface is upon the whole of a 

 curved form, with the concavity of the curve directed upwards ; but 

 the regularity of the curve is interrupted by a step or ledge, which 

 .runs in the long axis of this face, parallel with the concentric rings 



