C— GEOLOGY. 77 



it is pointed out that the anthracite condition, instead of being accom- 

 panied by a high ash-content — which is what might be expected if the 

 asli ratio were determined simply by the reduction in the non-ash— is 

 shown statistically io bear the reverse relationship. That is, the more 

 anthracitic the roal, the lower the ash. From this it is argued that the 

 anthracites of South Wales were formed of plant-constituents different 

 from those contributing to the steam and house coals. This proposition 

 gains no support from the study of the plants found in the associated 

 measures, nor does it explain why the coals of other fields, composed 

 in their various parts of very diverse constituents, do not exhibit the 

 anthracite phase. But the ash question needs to be approached from 

 another point of view. The ash of coal may, as I have shown else- 

 where, be composed of three entirely distinct and chemically different 

 materials. There may be (1) the mineral substances belonging to the 

 plant-tissues ; then ('2) any detrital mineral substances washed or blown 

 into the area of growing peat; and, finally, the sparry minerals located 

 in the lumen of the cleat. As to the first, I have long considered that 

 the coal was in large measure deprived by leaching of much of its 

 mineral substances ; it is otherwise difficult to account for the almost 

 total absence of potash. The second — detrjtal matter — is probably 

 present in some though not in all coals; the high percentage of alu- 

 minium silicate is probably of this origin. But the third constituent — 

 the sparry matter — may, both on a priori grounds and upon direct evi- 

 dence, be assigned a very important role in the production of the ashes 

 in most coals. 



When a coal with a strongly developed cleat is examined in 'large 

 masses it is at once seen that the cleat spaces are of quite sensible 

 width, and that they are occupied most commonly by a whit© 

 crystalline deposit which may consist of either carbonate of iron or 

 carbonate of lime, and there are also in many seams crystals of iron 

 sulphide — either pyrites or marcasite. These sparry veins may be as 

 much as -^j^th of an inch, or even more, in thickness, and they clearly 

 constitute the principal contributors to the ash. It has been suggested 

 that they are true components of the original peat, a proposition to 

 which no botanist would assent, and it appears certain that the veins 

 consist of material introduced by percolation from the overlying 

 measures, subsequent to the production of the cleat. If that be so, 

 it then will follow that the amount of the material present in coal must 

 be in some dii'ect proportion to the available cleat space, and if there 

 is no cleat neither will there be any vein-stuff to contribute to the ash 

 It should be pointed out that ordinary bituminous coal broken into 

 minute dice and washed so as to remove any heavy mineral particles 

 is found to contain a percentage of ash quite comparable with that of 

 an average anthracite. It is to be concluded, therefore, that the varia- 

 tions of the ash contents of a coal are no indication of the plant- 

 constituent of the coal. 



I have sought to show how the concept of the Coal Measures with 

 their sandstones, shales and coal-seams accords entirely with what we 

 know of modern swamps and deltas, and that just as each Coal Measure 

 fact finds its illustration in mndern conditions, so we may, inverting 



