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VI. On the Structure of certain Limestone Nodules enclosed in seams of Bituminous 
Coal, with a Description of some Trigonocarpons contained in them. 
By Joseph Dalton Hooker, M.D., and Edward William Binnev, Esq. 
Received November 23, — Read December 14, 1854. 
The specimens of plants which we are about to describe were found imbedded in 
nodules of limestone, enclosed in a thin seam of bituminous coal not above 6 inches 
thick, in the lower part of the Lancashire coal-field. Their relative position is best 
understood from the following section (in a descending order). 
1. Black shales containing Avicula papyracea, Goniatites Listeri, Orthoceras 
attenuatum and other Mollusca, apparently of marine origin. 
2. Bituminous coal enclosing a horizontal layer of limestone nodules containing 
fossil vegetable remains. 
3. Fire-clay full of Stigmaria Jicoides. 
The roof of the seam is also full of fossil shells, and those in the shales lie in imme- 
diate contact with the bituminous coal. 
The nodules of limestone occur at short irregular distances, and their size varies 
from that of a walnut to lumps weighing half a hundred weight. The smaller nodules 
are spherical, the larger are vertically compressed, being oval, compressed oval, 
cylindrical or flattened cylinders. The presence of the small nodules may be readily 
detected by the weight of the coal containing them, whilst the larger ones cause the 
coal to bulge out, both in the roof and floor of the mine. The surfaces of the nodules 
are extremely hard, but frequently present faint traces of lamination, or more rarely 
of concentric foliation. 
An examination of the surface offers very little indication of the fossil contents of 
these nodules, except that iron pyrites is more abundant in those conVdmmg Halonia, 
Lepidodendron and Stigmaria, causing in some instances a partial decomposition of 
the fossils. 
The origin of these nodules may probably be ascribed to the presence of mineral 
matter, held in solution in water and precipitated upon, or aggregated around certain 
centres, in the mass of vegetable matter now for the most part turned into coal. The 
effect of this has been to preserve certain portions of the mass from becoming bitu- 
minous and to produce their calcification. We however offer this explanation with 
considerable diffidence, being aware that the whole subject of the formation of 
nodules of one mineral in a matrix of another, is one that involves many considera- 
tions, and shall therefore confine ourselves to remarking, that the appearances are of 
MDCCCLV. Y 
