Rajmahál hills, besides their occurrence in the fields of Rániganj and Rámghar.
The Damúda series, thus named from its extensive development on the banks of the river Damúda, comprises, with perhaps one exception, all those rocks from which coal has been obtained in Bengal; the coal bearing rocks of the Himalaya, Khasi hills and Burma being, however, distinct. This series is divided in the Rániganj field by a mass of black shales, containing beds of clay ironstone, and attaining a total thickness of about 1,500 feet. There is evidence of unconformity between these shales and the Lower Damúdas, but none is clearly made out between them and the upper series or Rániganj beds, with which they are in consequence classed.
The Upper Damúdas of Rániganj must be carefully distinguished from those beds in Central India which have been called Upper Damúdas,[1] Mem. Geol. Survey of India, Vol II. pp. 176, 312. The Rániganj beds differ from the Lower Damúdas in mineral character, and also slightly, so far as is at present known, in fossil remains. The upper beds consist mainly of very thick false bedded sandstones, with seams of coal frequently continuous over considerable areas. The lower beds are much coarser and more conglomeritic, and are rarely false-bedded; their coal seams are numerous, but very variable in quality, and frequently thin out, or change into shale, or even sandstone, within very short distances.
The most characteristic fossil distinction between the two groups consists in the abundance of a species of plant referred by Mr. Oldham to Schizonema, in the upper division, which has not been found in the lower. No animal remains have as yet been discovered in the Damúda beds.
The upper or Rániganj series is not known to be represented beyond the Damúda field. The lower group is also found in Orissa, and along the Western side of the Rájmahál hills. The superiority of the coal of Rániganj is perhaps partly explained by the circum-
- ↑ This name was given for good geological reasons, as will be seen by reference to Vol. II. of the Memoirs of the Geological Survey. It has however proved an unfortunate appellation, as it conveys an incorrect idea of the relations of the beds, which contain a flora completely distinct from that of the true Damúdas, see Mem. Geol. Survey, Vol. II. p. 176.
