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cumbent shales, which were full of fossil shells supposed to be of 

 marine origin, and the aggregation of the mineral matter round 

 centres of vegetable remains. The chemical constituents of the 

 nodules were found to be carbonates of lime and magnesia, sesqui- 

 oxide and sulphate of iron, with a little carbonaceous matter. 



The probability of these nodules representing an average sample 

 of the vegetable constituents of the surrounding coal is then dis- 

 cussed, and attention is drawn to the very great interest and import- 

 ance that would attach to them were such a view substantiated, as 

 showing the exact nature of the association of plants which is 

 capable of conversion into bituminous coal. 



All the plants contained in the nodules were common in other 

 parts of the coal formation, viz. Calamodendron, Halonia, Sigillaria, 

 Lepidodendron, Stigmaria, Trigonocarpon, Anabothra, and others ; of 

 these the first-named genus occurred in the greatest abundance and 

 as large fragments of fossil wood. Very many of the specimens 

 were sliced, and being reduced to very thin transparent sections, 

 were examined with the view of determining the botanical character 

 of their contents, and the intimate structure of the masses of more or 

 less homogeneous aspect to which they were reduced by decompo- 

 sition, previous to or during the operation of calcification. The re- 

 sults were very satisfactory, and seemed to indicate that all traces of 

 vegetable structure may be completely obliterated in the substance 

 of highly bituminized coal, which may nevertheless also contain frag- 

 ments of wood with their tissues preserved. 



An account is then given of the examination of the details of 

 structure of Trigonocarpon, and this, as well as the comparison of 

 Trigonocarpon with the modern genus Salisburia, is illustrated by 

 drawings and analyses. 



The authors are still engaged with the study of these nodules, 

 with the view of showing the relationship between Calamodendron, 

 Calamites, Sigillaria and Anabothra, and the details are preparing for 

 publication. 



VOL. VII. 



