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



splits up with great ease into iudigo-blue and glucose, and 

 that this glucoside is probably, in all cases, the same, and 

 identical with the indican of Isatis tinctoria. 



Various other plants have been supposed to yield indigo- 

 blue. Of these I have examined the following : — 



Galega officinalis. 



Hedysarum Onobrychis (Sainfoin). 



Polygonum Fagopyrum (Buckwheat) . 



Polygonum Persicaria. 



Rhinanthus Crista-galli. 



Sophora japonica. 



Spilanthes oleracea. 



The leaves of these plants, when treated in the manner 

 above described, yielded no trace of any substance resem- 

 bling indican, and showed no indications of containing any 

 blue colouring-matter like indigo. 



XXIX. On Siliceous Fossilization. By J. B. Hannay, 

 F.R.S.E., Assistant Lecturer on Chemistry in the 

 Owens College. Communicated by Professor Roscoe, 

 F.R.S. &c. 



Eead March 19th, 1878, 



My friend Professor Young having mentioned to me that 

 certain questions connected with fossilization were in a 

 very undecided state, and having expressed his opinion 



