. F. Chapman — On Concretionary Nodules. 555 



and -018 mm. Some tourmaline and zircon crystals were also 

 present, probably derived from the acid igneous dykes of the 

 neighbourhood, and also I'emains of diatoms. 



These nodules differ in appearance from the irregular conci'etions 

 found in the estuarine swamps near Melbourne, in having an almost 

 circular outline, as if artificially rounded (so much so that the 

 workmen considered them to be ' faked '). From the occurrence of 

 tlie nodules on the sides of the old river channel, and seated in 

 depressions, we may reasonably assume that they received their 

 form in 'kettles' or 'potholes' in the clay bottom of the river bed, 

 within reacli of tidal influence. 



It was whilst examining the calcareous nodules from the old 

 Yarra channel that the writer was impressed with the close 

 resemblance they bore to the ' coal-balls ' of the Coal-measures in 

 England. The coal-seams of the Yorkshire and Lancashire 

 Coalfields contain calcai-eous nodules which include portions of 

 Coal-measure plants in a very perfect state of preservation. These 

 nodules vary in size, but are usually a few inches in diameter, and 

 more or less flattened. They are spoken of as 'coal-balls,' although 

 that term has also been applied to the rounded nodules of pure coal 

 having a concentric structure, which are met with in the coal- 

 seams of England, France, New South Wales, and elsewhere. The 

 former class of ' coal-balls,' however, are highly calcareous, being 

 composed of about 70 per cent, of carbonate of lime and magnesia, 

 and 30 per cent, of oxide of iron, sulphide of iron, etc.^ A great 

 interest attaches to these calcareous 'coal-balls' on account of their 

 having fui'nished the paleeobotanists Binney, Williamson, Scott, and 

 others with some of the best preserved Coal-measure plants upon 

 which they based their valuable observations. 



The general form of the nodules from the Coal-measures is 

 a flattened sphere ; and in this respect, amongst others, they 

 resemble the nodules from the Yarra. That the shape of the 

 ' coal-balls ' is due to segregation of carbonate of lime from the 

 overlying beds deposited radially and concentrically is open to 

 serious objection, since the nodules include pieces of Lepidodendron 

 stems, Calamitean roots, and other woody remains, which, by their 

 rod-like shape in the conglomerated mass of sticks and stems, would 

 tend to interfere with an incipient crystallization or segregation 

 acting from a central point. This idea of segregation in situ is, 

 however, the generally accepted one, and was clearly stated by 

 Professor T. Rupert Jones in his Presidential Address to Section C, 

 British Association Meeting at Cardiff in 1891,- in the following 

 words: — "The 'coal-balls' of Oldham, in Lancashire, and the 

 bullions at South Owram, in Yorkshire, are calcareous-carbonaceous 

 nodules in coal, having been formed by the infiltration of water 

 carrying carbonate of lime from the shells in an overlying shale 



1 See Cash &. Hick: Proc. Yorkshire Geol. and Polytech. Soc, vol. vii (187S- 

 1881), p. 73. Also Seward : " Fossil Plants," vol. i (1898), p. 85. 



• Report, 1892, p. 13. See also D. H. Scott: " Studies in Fossil Botanv," 1900, 

 p. 11. 



