TRANSACTIONS OF SECTION C. 435 



11. The Micro-Structure of Coal. By Dr. G. Hickling. 



The author stated that his chief aim was to establish the thesis that coal 

 is essentially a ' replacement ' deposit, consisting of an originally peat-like mass 

 of vegetable debris, in which the substance of the component tissues has been 

 largely or wholly replaced by the liquid decomposition-products of other vegeta- 

 tion. This conclusion is primarily based on the examination of typical ' bitu- 

 minous ' coals, in which nearly the whole substance of the coal is transparent 

 and orange- or brown-coloured in good sections. In this material vegetable 

 structure is often shown, sometimes in surprising perfection, with the cell- walls 

 uncrushed. The cell-cavities in such tissues are filled with the same material 

 which forms the main mass of the coal, and since the amount of this material 

 must be .several times greater than the original (dehydrated) organic content of 

 the cell, there can be no doubt that it is material secondarily introduced. 

 Further, since it pervades extensive masses of tissue with the cell-walls intact, 

 there can be no cjuestion as to the conclusion that it was introduced as a fluid 

 penetrating the cell-membranes. The only visible differentiation in the .sub- 

 stance of such coal is that due to variation in depth of colour. In this way 

 'cell-walls' are distinguished from 'cell-contents,' but commonly, as the tissue 

 is followed in one direction or another, the differentiation of walls and contents 

 decreases and finally vanishes, whence the tissue merges in an apparently 

 structureless mass. It appears probable that nearly the whole of such a coal 

 consists of 'replaced tissues,' in only a small proportion of which there is 

 sufficient differentiation to render cellular structure visible. 



The deptli of colour of the coal substance was shown to increase with 

 increasing carbon-percentage, as indicated by tlie streak, which varies from 

 pale brown in coals with 70 per cent, carbon to black in those with 95 per cent. 

 Hence it is increasingly difficult to prepare transparent sections as the carbon- 

 content rises. Cjreat variation, however, is found in the degree of uniformity 

 or otherwise of the coal-substance. Typical ' bituminous ' coals tend to be homo- 

 geneous, while cannels and canneloid coals are characterised by the association 

 of an opaque or very dark-coloured ' base ' ( ? of high carbon-content) with 

 abundant pale-coloiu-ed bodies, usually spores or the ' algne ' of Bertrand and 

 Renault (? of low carbon-content). 



The recognisable plant-structures present in coal include cortical tissues, 

 wood, leaves, isolated cuticles and spore-coats. Unbroken pieces of tissue of 

 considerable size are scarce, a minutely fragmentary condition being general. 

 The individual fragments are almost always lenticular, from the effect of com- 

 ))ression combined with an always present flow-structure. No indication has 

 been found to show that high-carbon coals differ in original vegetable con- 

 stituents from low-carbon coals. 



True woody tissues are commonly preserved as ' mother-of-coal,' in which 

 the lumen of the vessels is still empty or filled with secondary mineral matter, 

 the walls being converted into opaque material. No other type of tissue has 

 been certainly found to exhibit this type of preservation. 



Evidence was bi'ought forward to show that, whatever may be the true 

 nature of the ' algae ' described by Bertrand and Renault in cannel and similar 

 coals, they cannot in all cases be regarded as spores, as some recent authors 

 have suggested. 



12. On the Ecuiiuiiiir Mliirnil rroducts oj Diuiiandaiul , .S'.li'. Africa. 



By Thomas Ceook. 



13. Report on the Preparation of a List of Characteristic Fossils. 



See Eeporls, p. 116. 



14. Bepnrl on the Nnwenrlalnre of the Carboniferous, etc., Ttnelcs of 

 the Southern Hemisphere. — See Reports, p. 263. 



