416 Transactions. — Geology . 



annual growth-rings, the medullary rays, and the vascular tissue being 

 easily seen. Their crystallization is quite peculiar, differing entirely from 

 reef-quartz in being vesicular, or something like what snow is to ice ; and 

 much softer than rock-quartz, so that in many cases they can be scratched 

 with a knife. They are all flat-shaped, or knot-like ; just as if they had 

 been originally pieces of bark, or knees, or resinous knots, which had 

 resisted the action of ordinary putrefaction long enough to become com- 

 pletely silicified. 



Specimens are found showing the different stages of the process, from 

 lignite to perfect quartz. The small set accompanying this paper may be 

 referred to and described. No. 1, from the Hokonuis, in conglomerate, is 

 unmistakable wood, evidently a root of black pine {Podocarpus sjncata) or 

 kowhai (Sophora tetraptera). It is very hard, rings like clinkstone on being 

 struck, and is dark blue in colour, evidently from the carbon not being quite 

 oxidized out. In this respect it is exactly like a clay pipe when insuffi- 

 ciently burnt, part of the carbon of the nicotine remaining in the form of 

 soot to stain the pipeclay blue. In every respect this specimen is perfect 

 stone, giving sparks with steel, and with a specific gravity equal to quartz. 

 Its perfect woody structure and charcoal colour alone betray its origin. In 

 time the blue colour would no doubt have given place to white or grey, when 

 the last vestige of its carbon had been oxidized to C0 2 . No. 2 is from the 

 top of the coal at the Nightcaps, and shows the wood first changed to lignite, 

 on the under side, while the upper, or that exposed to the atmosphere, 

 is becoming white, hard, and qnartz-like, with a burnt appearance. No. 

 3 from the same locality shows this burnt appearance to such a degree 

 that one would conclude on looking at it that it had been through the 

 fire. Such, however, could not have been the case as it was detached 

 from the solid seam by the writer. 



These specimens show that carbon gets away from wood remains in all 

 probability as C0 2 by slow combustion at ordinary temperature ; and when 

 silica is supplied in the same proportion by highly silicated water, the 

 condition has in all probability been attained for the preservation of the 

 structure, after every other trace of its original has disappeared. 



Had the water absorbed by the decaying timber been unable to supply 

 the silica in the proper proportion to replace the carbon as it oxidized, 

 caverns in the quartz would probably have been formed, or a vesicular 

 structure, if more nearly equal to the demand, — just what is often observed 

 in these specimens. If the supply of silica was in exact proportion to the 

 departing carbon, perfect opal would be the result; while if from increase 

 of temperature from any cause, fermentation and putrefaction set in, the 

 carbon would get away so rapidly that no silicification could take place, 



