MR, J. B. HANNAY ON SILICEOUS FOSSILIZATION. 33 



explain how the rods came to be so easily dissolved. This 

 is a photograph of a hollow where a rod has lain which still 

 contains some rounded nodules of silica. It will be seen 

 from my former paper that these nodules are anhydrous 

 inorganic silicaj crystallizing out of the hydrated silica 

 after the rod has undergone a little dehydration since it 

 was alive. Now here we see the whole rod dissolved except 

 such portions as were entirely mineralized^ if I may use 

 such a term ; so that the reason the silica rods were so 

 easily dissolved by the calcareous solution was because 

 the silica of which they were composed was in a hy- 

 drated easily soluble form. Thus the existence of those 

 nodules which had before puzzled naturalists now gives us 

 the clue to the state of the rods at the time of solution. 

 Fig. 4 will still further elucidate this subject. Here it will 

 be seen we have a large number of rods partially dissolved. 

 I have examined^ by the means given in my former paper, 

 above twenty samples of these partially dissolved rods, 

 and I have not found one sample containing water ; so that 

 again we see the whole of the thoroughly mineralized 

 silica is left behind, and those portions which were very 

 probably hydrated dissolved. I say very probably; for we 

 see that the solvent action has gone on in a very irregular 

 manner, and in a manner which could not be accounted for 

 on any circulation-hypothesis, but just in such a manner 

 as would be caused by the irregular manner in which the 

 rods get mineralized. 



It might be expected that, since the rods were so neatly 

 and perfectly dissolved out, the spaces might get filled up 

 with carbonate of lime and reproduce the silica rod as a 

 calcareous fossil; but, although I have examined some 

 hundreds of these fossils, I have not found one case of this 

 nature. The only case I have found even approaching 

 to this is, that when the centre of the rod is dissolved it is 



SER. III. VOL. VII. D 



