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CALCAREOUS NODULES (‘ COAL BALLS ’) AND 
THEIR SIGNIFICANCE. 
R. CROOKALL, D.Sc., PH.D. 
Calcareous nodules (‘ Coal balls ’) are of great importance, 
both in palaeobotany and in the study of Palaeozoic and other 
coals. From them deductions can be made relative to (i) the 
structure and affinities of the fossilised plants they contain ; 
(2) the climatic and ecological conditions under which the 
plants lived ; (3) the mode of accumulation of the vegetable 
debris which formed the seams of coal, i.e. whether the remains 
of the (clearly land) plants accumulated on the spot where they 
grew or whether they were drifted by water and collected under 
the water-cover of a lake, lagoon or estuary ; (4) the origin of 
part of the ash in coal ; and (5) the approximate original thick- 
ness of the plant debris which eventually formed the coal-seam. 
Description.—' Coal balls ’ are irregularly spherical or 
ovoid stones which occur either singly or in masses in asso- 
ciation with some few seams of coal. They vary in size from 
that of a pea to several feet in diameter, but are most frequently 
of about the size of a potato. 
Both in Britain and in Holland large masses of these 
nodules may locally occupy the whole thickness of the coal- 
seam and weigh upwards of two tons. The bedding planes of 
the enclosing coal arch over the ‘ coal balls ’ (the latter 
offered greater resistance to pressure than did the coal) . Mr. J. 
Lomax has described an exceptionally large mass. From 
the thickness of the ‘ coal balls ’ compared with that of the 
adjacent coal, he concluded that 11 to 12 feet of vegetable 
debris had been transformed to form each foot of coal. 
Occurrence.— In Britain ‘ coal balls * were first found 
in the Upper Foot Coal of Lancashire and the Halifax Hard 
Bed of Yorkshire, low down in the Lower Coal Measures. 
They also occur in the Gannister Coal (beneath the Upper 
Foot) and at Stalybridge and Hough Hill in a small seam 
below the Gannister. At Laneshaw Bridge they are found 
in a seam in the Millstone Grit, while the Seven-feet seam of 
Wirral Colliery has also yielded them, i.e. Middle Coal 
Measures. Recently, a few ‘ coal balls ’ have been discovered 
in the Lower Carboniferous of Haltwistle, Northumberland. 
Abroad, ‘coal balls’ are known from the Carboniferous 
rocks of Spain, Russia, Moravia, Westphalia, Holland, the 
United States of America, and New South Wales. Dr. Stopes has 
described nodules from the Cretaceous of Japan which showed 
resemblances to, but also differences from true ‘coal ballls.’ 
‘ Coal balls ’ are found in three situations relative to the 
coal seam. ‘ Floor ’ nodules occur, somewhat rarely, in the 
fireclay floor of the seam. ‘ Seam ! nodules are found 
scattered irregularly throughout the coal itself ; they are 
1933 Nov. 1 
