48 DESCRIPTION OF FOSSIL TREES DISCOVERED 



insoluble state. About one-half of the mass of both consists of silica in a 

 crystallized state (common quartz crystals), presenting Jn the cavities beau- 

 tiful groups of crystals of the common form. The cavities in the High 

 Heworth tree are more frequent and regular, forming parallel fissures, sepa- 

 rated by thin walls of a more compact body, running in the direction of 

 the fibres of the original wood. Under the microscope, the more compact 

 part, portions of which occur here and there of considerable size, is seen to 

 be composed of similar crystals, embedded in a brown amorphous substance. 

 This brown substance prevails more in some parts of the fossil than in 

 others ; a difference due probably to the manner in which the decay of the 

 wood took place, but shewing that any two portions of the fossil taken with- 

 out selection, must vary considerably in composition. With acids, this so- 

 lid portion exhibits no effervescence, nor is it dissolved by long digestion ; 

 the lime only, and a small quantity of iron, being taken up by this treat- 

 ment. Reduced to a state of coarse powder, which contained necessarily 

 many fragments of the crystallized quartz, a portion of the Wideopen fos- 

 sil gave one per cent., and of the High Heworth fossil one-half per cent, of 

 carbonate of lime. The rest consisted of silica, a variable portion of alumina, 

 and two or three per cent., probably, of peroxide of iron. As the whole fossil 

 is a mixture only of these different substances, of which silica is the predo- 

 minant ingredient, forming perhaps four-fifths of the whole mass ; and as it 

 would be nearly impossible to obtain any part of the compound or amor- 

 phous portion free from crystallized quartz, any analytical attempt to esti- 

 mate the relative proportions of these ingredients would be useful only in 

 regard to the fragment actually reduced to powder and analyzed ; any other 

 portion would be likely to give very different results. I have, therefore, 

 considered it sufficient to determine that the lime forms a very small, and 

 the siliceous matter a very great, proportion of the whole substance." 



It has been shewn that the composition of the fossil-trees found in the 

 mountain limestone series, differs essentially from the above, lime instead 

 of silica being the predominating ingredient. This circumstance, besides 

 its interest in a strictly scientific point of view, might be rendered useful to 

 the practical investigator, it being obvious, that, in a sandstone deposit, of 



