MINERALIZATION OF ORGANIC REMAINS. 
67 
and not the internal organization; but there is another de¬ 
scription of petrifaction by no means uncommon, and of a 
much more wonderful kind, which may be compared to cer¬ 
tain anatomical models in wax, where not only the outward 
forms and features, but the nerves, blood-vessels, and other 
internal organs are also shown. Thus we find corals, origi¬ 
nally calcareous, in which not only the general shape, but 
also the minute and complicated internal organization is re¬ 
tained in flint. 
Such a process of petrification is still more remarkably ex¬ 
hibited in fossil wood, in which we often perceive not only 
the rings of annual growth, but all the minute vessels and 
medullary rays. Many of the minute cells and fibres of 
plants, and even those spiral vessels which in the living veg¬ 
etable can only be discovered by the microscope, are pre¬ 
served. Among many instances, I may mention a fossil tree, 
seventy-two feet in length, found at Gosforth, near New¬ 
castle, in sandstone strata associated with coal. By cutting 
a transverse slice so thin as to transmit light, and magnify¬ 
ing it about fifty-five times, the texture, 
as seen in Fig. 53, is exhibited. A text¬ 
ure equally minute and complicated has 
been observed in the wood of large 
trunks of fossil trees found in the Craio;- 
leith quarry near Edinburgh, where the 
stone was not in the slightest degree 
siliceous, but consisted chiefly of car¬ 
bonate of lime, with oxide of iron, alu- Section of a tree from the 
mma, and carbon, ihe parallel rows (Witham), showing text- 
of vessels here seen are the rings of an- ureofwood. 
nual growth, but in one part they are imperfectly preserved, 
the wood having probably decayed before the mineralizing 
matter had penetrated to that portion of the tree. 
In attempting to explain the process of petrifaction in 
such cases, we may first assume that strata are very gener¬ 
ally permeated by water charged with minute portions of 
calcareous, siliceous, and other earths in solution. In what 
manner they become so impregnated will be afterwards con¬ 
sidered. If an organic substance is exposed in the open air 
to the action of the sun and rain, it will in time putrefy, or be 
dissolved into its component elements, consisting usually of 
oxygen, hydrogen, nitrogen, and carbon. These will readily 
be absorbed by the atmosphere or be washed away by rain, 
so that all vestiges of the dead animal or plant disappear. 
But if the same substances be submerged in water, they de¬ 
compose more gradually; and if buried in earthj still more 
