COMPOSITION OF SOME WOOD ENCLOSED IN BASALT. 157 
The lime and magnesia evidently exist as carbonates; a small 
quantity of the protoxide of iron may also exist in combination 
i nic acid, as there is ‘28% of carbonic acid left after con- 
verting all the lime and magnesia into carbonates. The alumina 
and iron probably exist in the form of silicate, as the amount of 
silica is nearly sufficient to form a silicate of the formula R,0,, 
38i0., or if the water also be taken into account, Al,0,3Si0, 
20. 
s it contains traces of sulphur and of sulphuric acid, small 
quantities of iron pyrites are probably present. 
The combined water was determined by heating the powdered 
substance in a combustion tube and collecting the water in a 
weighed chloride of calcium tube, and the carbon by combustion 
filled first, the cell walls were next gradually removed, except those 
portions represented by the small remaining quantity of graphite- 
carbon, and replaced by mineral matter as the decay went on, 
so slowly and quietly that no violence was done to the micro- 
Scople structure of the woody tissue. 
