68 SECTIONAL ADDRESSES 
researches would yield interesting results in what we may call the study 
of micro-floras, but the work of collecting, naming and recording such 
great numbers of fossil plants will only attract a worker who has the 
appropriate opportunities for obtaining the information, and the patience 
of enthusiasm. 
Equal skill and patience was required for the second line of research 
indicated above. ‘The tabulation and analyses of the relative abundance 
of fossil spores, in one and the same coal seam, has been used to correlate 
beds in different parts of the Yorkshire Coal Field. A considerable 
degree of success has attended the method. Diagrams have been con- 
structed representing the spore index for different types of spores from 
top to bottom of selected seams, and, as a result, Mrs. G. E. Finn *° has 
been able to recognise individual seams of coal over distances of about 
40 miles, and independent of the flora or fauna of the associated rocks. 
The method was tested rigorously for the Arley, Better Bed and Silkstone 
seams with marked effect ; and it shows that the spore content and pro- 
portion of types of spore to one another can be relied upon for the identi- 
fication of seams in all parts of the Yorkshire Coal Field. 
Still thinking of single seams, the new technique of Hickling and 
Marshall 8? opens up another avenue for the use of plants in geology. 
They find that they can identify certain bark structures in Lepidodendron, 
Sigillaria and Bothrodendron by examining the thin layers of bright coal 
that often form the surface layer of the specimens. Having identified 
the types of bark, they go on to examine the layers of the coal itself, and 
it certainly appears that we may soon know accurately the plants that 
made the actual coal, whether the bark, wood or spores, and in what 
proportions they have occurred. 
The application of the metallographic method to polished and etched 
surfaces of coal has also yielded valuable results, as has been shown by 
Seyler.38 In these several ways the stigma of uselessness may yet be 
entirely removed from fossil plants as means of close zoning in the Coal 
Measures, and as indexes of definite conditions of accumulation of indi- 
vidual seams. The economic consequences may be equally important 
in the exploitation of special seams. 
Nor has the importance of the flora of Carboniferous age been confined 
to land and swamp plants, the marine algze have been extensively employed 
by Prof. Garwood in this country, and by other workers abroad, as 
zonal indexes. They have been employed as indicators of conditions of 
depth, and it is extraordinary the extent to which similar lagoon conditions 
had spread, for example, over the north of England and southern Scotland 
in early Carboniferous times. Sir Douglas Mawson, as already mentioned, 
has shown the wide spread of calcareous algz of the blue-green type over 
saltmarsh areas in Australia to-day *°; and this forces one to remember 
that the mere presence of algz does not necessarily imply marine lagoonal 
phases. Only when they are associated with actual marine animal forms, 
36 University of Sheffield Library, M.Sc. Thesis, 1931. 
37 Trans. Inst. Mining Engineers, vol. lxxxvi, 1933. 
38 Phil. Tvans. Roy. Soc., vol. ccxvi, 1928. 
39 Toc. cit. 
