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



per-cent, solution of caustic soda in a sealed tube to a tem- 

 perature of 110° C, so that they were under pressure, the 

 recent rods dissolved in about ten minutes ; No. II. was 

 nearly all dissolved in thirty minutes, leaving only a thin 

 core of anhydrous silica; while after two hours No. III. 

 was only irregularly eroded and in some places seemed 

 very little affected. On heating the three specimens to 

 100° with water for two days, very little change was ob- 

 served ; in fact water at the boiling-point was found to be 

 without practical eflPect ; but when heated to 150° C. in a 

 sealed tube, so that it was under a pressure of several 

 atmospheres, the water had the effect of making No. II. 

 much more transparent. It seemed, then, that at this 

 high pressure the substance took up water, and so was 

 rendered more similar to the recent sponge rods. I found, 

 however, that if a substance like ether, which boils at a 

 much lower temperature, were introduced into the tube 

 above the water, so that the pressure would increase much 

 more rapidly than with water, the rods might be hydrated 

 at a lower temperature. On heating the rods by themselves, 

 No. I. gave off water and became friable, sometimes exfo- 

 liating, No. II. also gave off water and became opaque like 

 No. III., and at the same time friable, while No. III. 

 underwent no change. 



The general conclusions to be drawn from these experi- 

 ments are that the principal difference between the three 

 kinds of rods lies in the relative proportions of water they 

 contain, and that the larger the proportion of water con- 

 tained in any sample the more transparent is it. Prom even 

 a cursory examination of the rods it may be seen that as the 

 proportion of water decreases the original features of the 

 rods become more and more obliterated, so that a totally 

 dehydrated rod is reduced to a mass of crystalline inorganic 

 silica. It will be seen that an examination of the state of 



