Vol. 58. | CONCRELIONS 1N THE LOWER COAL-MEASURES, 49 
One or two points may now be taken into account. First, that the 
calcium-carbonate was introduced in the state of solution, and by 
osmosis passed through the cell-walls, and was deposited within the 
cell-walls before their decay. (As a matter of fact, the cell-walls are 
still largely organic, as may be seen by treating the material with 
hydrochloric acid and examining the residue under the microscope.) 
Secondly, that the calcium-carbonate must have been produced in 
small quantity and deposited slowly, as shown by the isolation of 
the nodules and by their comparative rarity. Thirdly, that certain 
conditions were favourable, as the concretions are not found in every 
seam of coal. 
We have to consider in the first place why calcium-carbonate was 
produced in this coal, and also, in the second place, why it separatea 
out in the spherical form. 
Coal appears to have been formed by the slow decay of vegetable 
matter either in the delta at a river’s mouth or on a sea-shore. 
There is no formation being produced at the present day which 
exactly represents the conditions that existed in Carboniferous 
times ; hence it is difficult to trace out exactly what did take place 
so long ago. There is, however, sufficient evidence in the Coal- 
Measures to show that coal was produced by the decay of a very 
luxuriant vegetation upon swampy ground, which at certain periods 
was covered by inundations both of brackish and of salt water. The 
freedom of the coal-seams from all but the finest mud, shows that 
the vegetable matter was clotted together so closely as to exclude 
all but the very finest mineral impurities in suspension, while 
allowing the free circulation of the water with its matters in 
solution. Brackish water being simply diluted sea-water, the salts 
in solution would be those present in sea-water. 
The late Prof. Dittmar’ and others have made numerous exhaustive 
analyses of sea-water collected during the Challenger Expedition, 
and the following figures represent the average proportion of ~e 
different salts :-— ud 
| Per cent. jn 
Somiumrenloride: 6 s.7.8c...ssscce 77758 cacy ti" 
Magnesium-chloride ............... 10°878 ‘ 
Magnesium-sulphate ............... 4-737 
Caleciumesulphaté: 2. c220...0205. <>: 5°600 
Potassium-sulphate ............... 2'465 
Magnesium-bromide .. ............ 0-217 
Caleium-carbonate .............-. 0345 
100-000 
Sea-water contains 3°5 per cent. of total salts, hence the amount 
of calcium-carbonate in the sea-water is ‘012 per cent., and that 
of calcium-sulphate ‘126 per cent. According to T. E. Thorpe & 
KK. H. Morton,” 1000 grammes of sea-water contain ‘04754 gramme 
of calcium-carbonate, and ‘00503 gramme of ferrous carbonate. 
teturning to the formation of coal, we may picture to ourselves 
’ Challenger Reports: Physics & Chemistry, vol. 1 (1884) p. 204. 
* Journ. Chem. Soe. vol. xxiv (1871) p. 507. 
@.J.G-8. No, 229. E 
