MR. J. B. HANNAY ON SILICEOUS FOSSILIZATION . 



237 



combination of the water in the different rods would be 

 likely to throw light on their constitution ; but^ owing to 

 the small quantity of rods at my disposal, the method for 

 thus examining substances, which I have published else- 

 where*, was in this case inapplicable, an optical exami- 

 nation being the method which promised to yield the best 

 results. Heating the rods with caustic-soda solution did 

 not give results throwing any light on their structure, the 

 general effect of this reagent being to erode them, as shown 

 in fig. I. An attempt was made to gain a knowledge of 



the structure of the rods by imbedding a specimen of No. 

 II. in Canada balsam so as to leave only one half exposed, 

 and then to etch away this upper portion by means of 

 hydrofluoric acid. This method succeeded pretty well, 

 giving a sectional view of the internal structure of the rod, 

 as shown in fig. 7, The layers are seen by this method 

 to be pretty clearly marked ; but the etching is very 

 irregular. 



The next method tried was rendering the opalescent 

 nodules transparent by means of high-pressure steam or, 

 rather, water, as the substance was always surrounded by 



* "Examination of Substances by the Time Method," Chem. Soe. Journ. 

 No. clxxTii. 



