MR. J. B. HANNAY ON SILICEOUS FOSSILIZATION. 31 



IV. On Siliceous Fossilization. — Part II. By J. B. Hannay, 

 r.R.S.E.^ F.C.S., Assistant Lecturer on Chemistry in 

 tlie Owens College. 



Bead March i8th, 1879. 



In a former paper it was shown^ by chemical and optical 

 means, that the fossil siliceous rods Hyalonema Smithii 

 were identical in constitution with those from modem 

 sponges, and that the curious nodulized appearance of some 

 of the rods was due, not to the original form of the rods, 

 but to certain physical and chemical changes which have 

 passed over them since they were deposited where they 

 were found. It was also shown that of the three forms of 

 silica, transparent, gelatinous, and opaque, the first and 

 second were easily acted upon and retained the original 

 structure of the organic silica, whereas the last was in the 

 truly mineral form and had lost every trace of organic 

 structure, and was not easily acted upon by chemical 

 means. Mr. John Young, P.G.S., having kindly supplied 

 me with several specimens o£ the fossils from the limestone 

 quarry at Kilwinning, which are very different from those 

 I previously examined, and which throw more light on the 

 changes which siliceous fossils may undergo, I beg to give 

 an account of them to the Society. One piece of limestone 

 simply contained (instead of rods) a number of cylindrical 

 holes where the rods had lain. In fig. i, which is a wood- 

 cut from a photograph, are seen these cylindrical holes, 

 which plainly show that the rods have been dissolved away. 

 The solvent must have been a strong calcareous or other 

 alkaline solution, as the calcareous fossils are not in the 



