410 On Spirally dotted Ducts in Anthracite Coal. 
7, As anthracite is only bituminous coal which has lost its 
volatile matter, the results obtained from it apply to all varieties 
of the true coal of the Carboniferous epoch. 'The presence of 
bitumen, however, and the consequent swelling and partial fusion 
of the ordinary coal, render it difficult to obtain from it the tissues 
in the perfection in which they may be found in anthracite. 
Fig. 1. 
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Fig. 5. 
Explanation of the Figures. 
Fig. 1, shows the appearance to the naked eye of a mass of partly 
burned anthracite, on which the vascular.tissue is found. The black 
portion is the unconsumed coal. The white portions represent the 
silica left after oxidation of the carbon. 
Fig. 2, shows the manner in which the vessels occur in successive 
superimposed layers. It also gives an idea of the general appearance 
of the tissue when moderately magnified; the black lines being the 
unburned coal, the white spaces being spots of silica. 
Fig. 3, is a sketch made by the camera-lucida, showing the appear- 
ance, as an opaque object, of a small portion of two ducts from anthra- 
eite, much magnified. The white irregular spaces are patches of silica; 
all the black lines represent unburned coal. 
Fig. 4, is a sketch made by the camera-lucida, showing the appear- 
ance, as a transparent object, of a fragment of a single duct from an- 
thracite, much magnified. The ovoidal spaces are thickened portions 
of the siliceous plate, and apparently correspond to the pits in the walls 
of the original tissues. 
Fig. 5, shows %;ths of a millimetre, drawn by means of a camera- 
lucida from a micrometer equally magnified with the two last figures. 
