194 PKOK. W. U. WILLIAMSON ON MINEKALIZATION. 



frequently when the strata in which the fossils are preserved 

 are shales and clays, like the Oxford clays and the Liassic beds 

 on the Yorkshire coast, in which many of the calcareous shells 

 of the Ammonites have been converted into iron pyrites, which, 

 in the old days, we used to call Sulphuret. The calcareous 

 shell is here replaced by this Sulphide of iron. Vegetable 

 substances are equally liable to be replaced by this Sulphide 

 of iron. I have on the table a specimen of a Stigmaria — one of 

 the Sigillarian and Lepidodendroid roots — where the Sulphide 

 of iron has taken the place of everything else. Sections of 

 these things are, under the microscope, as black as ink, but 

 with a common pocket lens you will be able to see minute 

 particles of this Sulphide of iron, not only covering the cell 

 walls on their outsides, but the solution of the metal has 

 passed, by osmosis, through cell walls, and in like manner 

 covered their inner surfaces, whilst in other examples the iron 

 has substituted itself for the vegetable substances. Whether 

 the whole of the organic carbon has disappeared I cannot 

 absolutely determine, but, so far as I can see, there is not a 

 trace of it left. I have tried, by making sections of some of 

 these specimens with a view of discovering whether or not any 

 traces of organic carbon were left, but this does not materially 

 affect the question under consideration. Examples of silicified 

 plants on the table show perfectly clearly there is no carbon 

 there, and it does not particularly matter whether there was 

 any left or not, because whilst in some all the original carbon 

 certainly disappears, in other cases it as certainly does not. 



The conclusion to be arrived at from this hasty treatment of a 

 very complex subject will be somewhat as follows : — Numerous 

 objects have either lived in water, or on land which has sunk 

 beneath water. As they died, their remains sank to the sea- 

 bed, and there they became imbedded in the sand, mud, or 

 whatever materials that floor consisted of. Those materials 

 became consolidated into limestone, sandstone, or shale, sand- 

 stone being but consolidated sand, whilst shale is mud so 

 altered, and limestone was, in large measure, Foraminiferous 

 and Coralline ooze. Enclosed firmly in one or other of the 

 above consolidated materials, as the sculptor prepares for his 

 metallic casting by enclosing his clay model within its plaster 

 mould, each organism underwent more or less of change. In 



