Vol. 65.] PLANT-CONTAINING NODULES FROM JAPAN. 205 



VII. SUMMARY. 



The nodules are of Upper Cretaceous age. 



They are concretions enclosing numerous marine shells and various 

 plant-fragments well petrified. 



They are not directly connected with any coal-seam, but lie in a 

 thick series of shales below the coals. 



In microscopic section the matrix appears highly granular, unlike 

 the. matrix of coal-balls and roof-nodules. 



Chemical composition includes roughly 60 per cent, of carbonates 

 and 30 per cent, of silicates, the large proportion of the latter 

 being an important point of difference from the Carboniferous 

 nodules. 



In having numerous plant-fragments in a single nodule, and in 

 the type of petrifaction, the nodules are like ' coal-balls ' ; in having 

 marine shells included in the matrix, they are like ' roof -nodules.' 



They probably represent fragments of tangled debris which had 

 drifted but a short distance out to sea, and were then speedily 

 petrified. 



This work was done while travelling in Japan with a grant from 

 the Government Grant Committee of the Royal Society. Very 

 material assistance was also rendered by the Imperial Japanese 

 Government through its Geological Survey, the Imperial University, 

 and the local Government of Hokkaido, as well as by the Tanko 

 Kaisha (Coal-Mine Company) of Hokkaido, without whose hearty 

 co-operation the work would have been hardly possible. To 

 everyone who has thus rendered valuable help, I here tender my 

 sincere thanks. 



EXPLANATION OF PLATE IX. 



Fig. 1. Microphotograph of a portion of the matrix of a plant-containing 

 nod ale, showing its highly granular nature. Magnified 30 diameters. 



2. Photograph of section through a nodule, showing s various scraps of 



shells, a an ammonite in transverse section, p plant-fragments, and 

 st transverse section of a plant-stem. Natural size. 



3. Microphotograph of part of a section through a plant-containing 



nodule, showing numerous small fragments close together : b — frag- 

 ment of leaf ; m=crystals of matrix ; s=clump of plant-sclerenchyma. 

 Magnified 20 diameters. 



4. Microphotograph of a transverse section of a stem preserved in a 



nodule similar to that shown in fig. 3. Magnified 20 diameters. 



Discussion. 



Prof. Garwood congratulated the Authoress on her interesting 

 discoveries in Japan, and regretted the lateness of the hour which 

 prevented the paper from being read in full ; he felt sure that, when 

 the paper was published, it would prove to be an important con- 

 tribution to the study of those interesting structures, ' coal-balls ' 

 and ' roof-nodules.' 



