O. W. Buhnan — Drift Coal in Sanddone. 151 



the currents regained their force. And we must suppose the same 

 currents brought down vegetable matter, which, when their force 

 failed, might be laid down among the coarser sediments, and would 

 at other times be carried beyond and laid down by itself. The 

 obvious inference is, that, as beds of pure shale are due to the same 

 drift origin as the fragmentary patches in the sandstone, so, if we 

 allow a drift origin for the fragmentary coal, we must also admit 

 the probability of the accumulation of beds of pure vegetable matter 

 by the same agency. 



But as in the case of shale we find every gradation between 

 included fragments in sandstone or shaly sandstone, and strata of 

 pure shaie, so — if the origin is the same — should we find a similar 

 series of transitions in the case of coal. And such is, in fact, the 

 case. For, as we have shaly, so we have carbonaceous, sandstones ; 

 and as we have shales intercalating with, and occurring as isolated 

 masses of considerable extent in, sandstone, so we find it also in 

 the case of coal. 



In the Survey Memoir of the Yorkshire Coal-field some good 

 examples of the complicated intercalations of shale and sandstone 

 are given (see pp. 73 and 94). These are similar to the intercala- 

 tions of coal and sandstone in connexion with one of the " rock 

 faults " described and figured in the Memoir of the South Stafford- 

 shire Coal-field. 



Reference to the sections (figs. 4 and 5) given on pages 184 and 

 185 of this latter Memoir shows the intimate connexion of the coal 

 and sandstone. And, as Mr. Jukes remarks, even the minute 

 veins of coal are " perpectly bright good coal." It is difficult 

 to account for this purity combined with intimate intercalation on 

 the theory of growth in situ, and the similarity to the intercalations 

 of shale above referred to suggest for the coal a similar origin. 



In the Coal-measures of Central France, again, M. Fayol describes 

 numerous examples of the minute intei'calations and interlaminations 

 of the coal with sandstone and shale. In their intimate ramifications 

 with the sedimentary deposits these portions of coal seams ai'e 

 strictly comparable to the intercalations of shale and sandstone of 

 the Yorkshire Coal-field, and to the branching of the "Thick coal " 

 in connexion with the " rock fault." And they form one of the 

 arguments which have led M. Fayol to advocate a drift oilgin for 

 the coal. 



Such intercalations of coal and sandstone, then, while they form 

 a difficulty on the hypothesis of terrestrial accumulation, are just 

 what we should expect if we ascribe to the coal an origin similar 

 to what we allow for the shale. 



The purity of the coal — even in the thin veins — and its clear lines 

 of demarcation from the sandstone can only be attributed to the 

 sorting power of water ; the hypothesis of floods carrying sediment 

 over the edges of the swamp where vegetation was accumulating 

 cannot account for this purity of the thin layers of coal ; for the 

 growth of vegetation after each flood would necessarily mingle itself 

 with the mud, and be in turn thoroughly permeated by that brought 



