Vol. 58. ] CONCRETIONS IN THE LOWER COAL-MEASURES. a5) 
have therefore the property of modifying calcium-carbonate as it is 
formed, and converting it into spheroids or rounded crystals. Any 
solid substance suspended in the liquid during the deposition acts 
as u nucleus, and this may be seen in the photograph of a cotton- 
fibre upon which nodules of carbonate of lime are forming (fig. 3, 
p-. 04). 
As peaty matter produces a result similar to that obtained with 
the colloids, it is fair to assume that the nodules from the Coal- 
Measures may have been produced in stagnant water containing 
a large quantity of organic matter in solution. But there is reason 
to believe that these nodules were the centres of bacterial activity, 
and that they grew in a true colloid—the bacterial jelly—which 
was attached to portions of the undecayed vegetable matter now 
found perfectly preserved in the fossilized condition. 
(2) On the Action of Salts of Lime sae of [ron upon 
Wood, etc. 
The experiments on the action cf salts of iron and of lime 
proved that soluble iron-salts are preservatives, arresting decay in 
vegetable matter and even in putrescent animal matter; whereas 
hme-salts did not prevent decay, moulds growing rapidly, and very 
soon woody tissues, etc. were destroyed. In no case, however, was 
there any approach to fossilization or the deposition of calcium- 
carbonate. 
When ircn-salts and sodium-carbonate were applied many times 
alternately, the wood became gradually harder and penetrated by 
ferric hydrate. When calcium-salts and sodium-carbonate were 
applied many times alternately, the cells became filled with crystal- 
line calcium-carbonate, and small nodules were formed on the 
exterior (see fig. 4, p. 54). 
Though interesting, this experiment reveals nothing as to the 
natural process of fossilization, for we know of no such mivernavion. 
in the crust of the globe. 
(3) On the Action of Bacteria upon Solutions containing 
Calcium-Sulphate, ete. 
In the third series of experiments, a solution containing sewage 
was mixed with calcium-sniphate solution and left for a few days; 
it quickly became black, and contained an immense number of 
bacteria. A solution of calcium-sulphate containing ferric hydrate 
in suspension (representing the calcium-sulphate of sea-water and 
the iron in the mud) was kept in a closed bottle with both fresh 
and decayed woody tissue and some decayed fish: the whole repre- 
senting on a small scale the conditions present in local areas during 
the formation of coal. After a year, the bottle was opened and 
examined. It was quite black throughout, and smelt strongly of 
