Geological Society of London. 109 
If introduced immediately on the first commencement of decomposi- 
tion, then the most destructible parts are lapidified, while the more 
durable do not waste away till afterwards, when the supply has failed, 
and so never become petrified. ‘The converse of these circumstances 
gives rise to exactly opposite results. As to the manner in which 
the minutest pores and fibres discoverable by the microscope, even 
the spiral vessels themselves, can be turned into stone, or have their 
forms faithfully represented by inorganic — no aonmen ex- 
planation has ever yet been offered. In wever, this 
question, you will do well to consult the important sogieetiin which | 
a celebrated chemist, our late lamented Secretary, Dr. Turner, has 
thrown out on the application of chemistry to geology. He reminds 
us that whenever the decomposition of an organic body has begun, 
the elements into which it is resolved are set free in a state peculiarly 
adapting them to enter into new chemical combinations. They are 
in what is technically termed a nascent state, the constituent mole- 
cules being probably of extreme smallness and in a fluid or gaseous 
form, ready to obey the slightest impulse of chemical affinity, so 
ibat if the water percolating a stratum be charged with mineral in- 
gredients, and come in contact with elements thus newly set free, ‘a 
mutual action takes place, and new combinations result, in the course 
of which solid particles are precipitated so as to occupy the place 
left vacant by the decomposed organic matter. In a word, all the 
phenomena attendant on slow putrefaction must be studied whenever 
Wwe attempt to reason on the conversion of fossil bodies into stone; 
and in regard to silicification, Dr. Turner has shown how great a 
quantity of silex is set free as often as felspar decomposes, and how 
abundantly siliceous matter may be imparted from this source _ 
to running water throughout the globe. wad 3 
As I have mentioned the name of Dr. Turner, te cannot pass on 
without an expression of sorrow for the untimely death of that ami- 
able and distinguished philosopher. Mr. Whewell in most feeling 
terms alluded this morning at the general meeting to this melancholy 
event, which is too recent and too painful to myself and others to 
allow me now to dwell longer upon it. 
Before quitting the subject of vegetable petrifactions, I ought to 
mention a memoir just published, by Mr. H. R. Géppert, Professor 
of Botany at Breslau, “On the various Conditions in which Fossil 
Plants are found, and on the Process of Lapidification.”’* He has 
* Poggendorff, Annalen der Physik und Chemie, vol. xxxviii. part 4. Leipsio, 
1836. . 
