COAL MEASURES. 1/9 



Concerning the strata among which the seams of coal occur, it 

 may be remarked that the shales known to the miners as ' binds' 

 or 'plate,' are more persistent than the sandstones, and they yield 

 some of the finest specimens of Coal-plants. 



The sandstones are very variable in character. Where they are 

 protected from the weather, they are usually blue or grey, and they 

 then contain iron as ferrous carbonate. Where exposed to the 

 atmosphere, they are frequently red or brown in colour. The 

 materials of which the sandstones are composed have in many 

 cases been furnished by the wear and tear of crystalline rocks, 

 such as granite. 



The Underclay is known as 'Spavin' in Yorkshire; as 'Thill' in 

 Durham ; as ' Warrant ' or ' Seat-earth ' in Lancashire ; and as 

 ' I^ottomstone ' or ' Pouncin ' in South Wales. The rocks grouped 

 under this head vary much in composition. Very frequently they 

 consist mainly of clay, but many of them (as in the Yorkshire coal- 

 field) are hard clayey sandstones. The most siliceous form, known 

 as Canister or Calliard, is a hard, close-grained siliceous stone. 

 The underclays are unstratified, and usually form the floor of a 

 seam of coal, but sometimes no coal occurs, when a seam of 

 carbonaceous black shale is usually met with. 



The hard seat-earth, known as Canister, though it is found in 

 the Millstone Grit, and is not altogether absent from the Middle 

 Coal-measures, occurs oftener in the Lower Coal-measures than 

 elsewhere among the Carboniferous rocks. One seam of coal, 

 distinguished as the Canister Coal, has almost invariably a Canister 

 floor. Hence the name Canister (or Cannister) Beds has been 

 given to the Lower Coal-measures.^ 



Amongst the fossils of the Coal-Measures may be mentioned the 

 following : — Plants, Stcnibergia and Noeggcrathia, belonging to the 

 group Conifcrce; Sigillatia, Lcpidodt'tidron, Lepidosirobus (fruit-cones), 

 UlodcndroJi and Asterophyllitcs belonging to the group LycopodiacecB ; 

 Calamites belonging to the group Equisetacccc; and the Ferns 

 Ale t hop ten's, Pecopteris, Neuropteris, Sphetiopteiis and Caulopteris? 



In the Lower Coal-measures certain marine Mollusca have been 

 found, including Avu'u/opec/en papyraceus, Spirifera pinguis, Productus 

 semireticulatus. Nautilus armatus, Gouiatites Listeri, Lingula squamosa, 

 Posido7iomya Gibsoni, P. Becheri, Conularia quadrisulcata, etc. La the 

 Middle and Upper Coal-measures the Mollusca include Afithracosia 

 and Anthracomya, forms usually regarded as belonging to fresh- 

 water; Anthracosia, however, may have been an estuarine shell like 

 Scrobicidaria. 



Among other fossils are the Annelide, Spirorbis pusillus {car- 

 honarius); Crustacea, Beyrichia, Estheria, Afithrapalcemon, Eurypterus, 

 Prestwichia, Beliniirits, Dithyrocaris ; Insects, including remains of 



^ A. H. Green, Geology of Yorkshire Coal-field, pp. 19, 25. 



- See J. Lindley and W. Hutton, The Fossil Flora of Great Britain, 1831-37 ; 

 and more recent memoirs by Sir J. D. Hooker, W. Carruthers, W. C. Williamson, 

 E. W. Binney (Palaeontograph Soc), and R. Kidston, (Catalogue of Palreozoic 

 Plants, British Museum). 



