MR. J. B. HANNAY ON SILICEOUS FOSSILIZATION. 241 



into the opalescent or semigelatinous-looking form No. 

 II.; and in so doing they begin to lose some of their in- 

 ternal structure; that is^ the layers adhere more closely, 

 and the rods become brittle and lose the glass-like flexi- 

 bility they originally possessed. At this point any further 

 loss of water causes crystallization to set in, the silica not 

 being able with a lower proportion of water to remain in 

 the " organic ^^ state; and if this crystallization sets in at 

 a great many points, the nodule soon becomes an opaque 

 mass of crystalline silica as in variety No. III. ; but if 

 crystallization sets in at comparatively few places and 

 spreads slowly out, it forms the kind of nodules drawn into 

 fig. 10. If at this point any solvent agent comes into 

 contact with the rod, it dissolves away the non- crystalline 

 portion, leaving nodules as shown by Dr. Young and in 

 fig. 1 1 ; but if no solvent action goes on, the rod 

 ultimately becomes transformed into variety III., which 

 is crystalline silica. 



The transformation from " organic " to " inorganic " 

 silica is one of arrangement; and as the ^' organic^' ar- 

 rangement requires a certain amount of water, whenever 

 the proportion falls below this a simpler arrangement sets 

 in, and we have crystalline silica. That the rods of Hya- 

 lonema Smithii are the same in constitution at least as 

 those from modern sponges is, I think, proved from these 

 experiments ; and to show a further analogy, I have drawn 

 a fractured specimen of such in figs. 4 and 5, the simila- 

 rity of which is very striking. 



SER. III. VOL. VI. 



