270 Calcareous Nodules (‘ Coal Balls’) and Their Significance. 
of salts was inexhaustible, for new water mingled continually 
with the old and brought fresh sources of mineral to petrify 
the plants. Thus in the heart of the masses of coal were 
formed large and small concretions of carbonate, some regular 
as balls and very large, others minute and uniting together 
to form wisps or sheets of stone lying in the coal. 
‘ The stony masses hardened, and as the weight above 
gradually pressed down the soft plants which would ultimately 
form the coal, they withstood the crushing uninjured, the 
delicate tissues embedded along with scraps of young plants 
which had but begun life, and were at once preserved alike 
from further growth and from decay. 
In the sea above, the currents carried fragments of plants 
from the neighbouring land, brought by the streams from the 
higher ground. These sank in the muddy floor and were 
gradually crushed by the silt collecting above them, till they 
were flattened as impressions in the beds which afterwards 
formed shales. Others, sinking upon the floor of the sea where 
the many decaying animals liberated so much carbon that the 
sulphates in the water were converted into carbonates, were 
slowly petrified — but not before the vicissitudes of their 
journey had partly destroyed and torn them, yet those of their 
tissues which escaped these ravages were so well preserved 
by the sea water that their every cell was petrified by the 
deposited carbonates, which formed concretions round them 
and enclosed at the same time so many shells. 
‘ These drifted plants, whether their fate was to be enclosed 
in the preserving nodules or to be crushed into the shales, 
had principally come from regions different from those which 
produced the half-formed coal now lying immediately below 
them. 
‘ Slowly they too were covered by the fine deposits which 
collected gently over them, until the sea bottom rose again 
to form a new land. All this time the plants were preserved 
in the coal balls without disturbance or hurt, and although 
the coal-forming debris had been pressed down into coal which 
was now but a foot in thickness, they remained uncrushed in 
their original form. 
‘ This has happened with slight variations many times in 
the course of the history of the world ; but only where the 
land rose and sank gently and the plants were covered as they 
fell in a still inlet of the sea. Where the plants were hurried 
down to sea and collected together swiftly and then covered 
by a sandy or estuarine deposit forming rapidly, there no 
“ coal balls ” are found. 
‘ Thus, the “ coal balls ” in the coal are the relics of a 
forest which grew quietly in a swamp in the place where they 
are now found, while the plants in the shales and in the roof 
The Naturalist 
