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 spicata) 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 CO, 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 quartz-like, with a burnt appearance. No. 
9 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 CO, 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, 
