On Sunday, November 24, 2002, at 06:33 pm, James Findlay wrote:
> Not sniggering but what are coal balls ? The only 'coal ball' I have
> seen was of a
> lump of coal that was caught in the return end of a belt line and was
> made perfectley
> round to the size of a large orange ! Some how I don't think this is
> what you mean.
> Any pictures ?
>
>
Hi James,
Coal balls are petrifactions in geological speak, basically a
concretion composed of calcium carbonate, some were very phosphatic
too. In the Lancs coal-field and then confined to certain
horizons/mines these concretions also managed to fossilise plant
material, including roots, branches, fruits, spores, all the botanical
'bits & bobs' that went to make up the Coal Measures plants and trees
species in fact.
Unlike the compressed fossil plant material often found on coal
surfaces or within the Seat Earth (ganister) the method of
fossilisation preserved the cell structure of the plants et al in
minute detail, depending on the chemical composition of the balls, the
more iron (pyrites) generally meant a less well defined fossilisation.
In shape they were usually ovoid to round and came in a whole range of
sizes, from very small, e.g. an inch or so in overall diameter up to
massive things two or more feet in diameter. In fact at one time they
were thought to have formed separately to the coal deposits and
'rolled' much like a pebble into situ, until someone found some which
enclosed tree trunks through them, other geological indicators
determined their growth in situ. Much like modern 'petrifying' wells
'work' in fact.
The method developed to study the plant material was to slice the
balls, some were then found to be chock full of remains, others barren,
the next stage was to grind a very flat surface on the interesting
looking specimens, etch in acid, which removed the carbonate, and left
the plant material standing proud. Next the surface was flooded with
acetone and a sheet of acetate laid on, after the acetone had
evaporated the acetate sheet could be 'peeled' (hence the term
'peels') off leaving the plant material embedded and available for
microscopic investigation.
A wonderful way to 'waste' time and great fun when slicing dozens of
balls in the ever expectant hope of finding something new, a bit like
cracking open geodes with all the 'excitement' of finding 'treasures'
within!
Unfortunately I don't have any of my books on paleo-botany to hand so I
can't send you a photo, although a web search may assist. I still have,
somewhere, my collection of peels taken from the Old Meadows coal
balls. The oldest land plants, found in Scotland in chert, also
fossilised in much the same manner, but getting peels or sections from
that material is another ball (sorry!) game altogether.
Hope that hasn't bored everyone rigid.
Peter Challis
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