204 miss m. c. stopes on [May 1909, 



of silicates of aluminium (clay), indicates clearly that the nodules 

 were formed in a region where detrital matter, from the neigh- 

 bouring rivers presumably, was being quietly deposited. The whole 

 area in this period was one of deposition ; the land was being built 

 up, and, not very much later, thick coals were deposited under 

 what seem to have been freshwater conditions. In the succeeding 

 beds no plant-tissues are petrified in concretionary nodules, nor are 

 there true coal-balls in the coal, as previous work led me to expect 

 from the apparent absence of marine conditions during its deposition. 



The fragments, brought down to the sea had the favourable chance 

 of petrifaction, without having drifted far enough to have been 

 scattered or destroyed ; then, as the land rose and the sea-water 

 was shut out, the succeeding debris formed coal, but no tissue- 

 petrifactions. 



It may be remembered that from the Carboniferous a single 

 'floor-nodule' was described from below the coal (Stopes & Watson, 

 op. cit. p. 180). This resembled the other nodules in the preser- 

 vation of plant-tissues, but had a larger proportion of clay among 

 its constituents : hence, it is possible that someone might suppose 

 this nodule to be homologous with the Japanese nodules. However, 

 this is not the case, for the ' floor-nodule ' had formed by segrega- 

 tion round the roots of the plants growing in situ, as was shown 

 by the nature of the petrifactions which it enclosed. The Japanese 

 nodules were formed round drifted fragments, which collected near 

 the shore some time before the deposition of the coals began. 



In a few words, one might conclude the matter by saying : — 

 Just as the ' roof-nodules ' contain plants which drifted out to sea 

 from a region where coal-deposition had been previously going on, 

 and, sinking, were petrified together with the shells of marine 

 organisms in nodules of concretionary nature ; so the Japanese 

 nodules contain plants which drifted but a short distance out to sea 

 from a region where coal-deposition would begin shortly after, and, 

 sinking, were petrified together with the shells of marine organisms 

 in nodules of concretionary nature. 



In neither case, probably, do the plants in these marine nodules 

 represent quite the same ecological community as that which later, 

 or earlier, formed the coals. It has been proved that the Carbo- 

 niferous nodules represent a flora of a somewhat different nature 

 from that in the coal, and so too in all probability the Japanese 

 nodules do not contain entirely the same plants as those which 

 later formed the coal. 



It is, in truth, more or less of an accident that there should be 

 coal-seams associated, either with the ' roof-nodules ' from the Car- 

 boniferous, or with the Cretaceous nodules. A chance that probably 

 depended, however, on some local facility of transport and deposition 

 which favoured coal-formation ; and the currents, before or after 

 they brought masses of plant-tissue sufficient to form coal, continued 

 to carry scattered fragments, which were preserved and petrified 

 with the shell-debris among which they accumulated. 



