VIII. — Economic Geology. 



Coal. 

 In the preceding pag-es it is indicated, as a rule, whether the coal. 

 External characters, at the outcrop, is 'hard^ or 'soft'. Thedistinc- 

 Hard coal. i\^q^ jg ^^ important one with reference to the 



market value of the fuel. The best hard coal is very homogeneous in 

 structure, with little or no 'cleat,' and without apparent lamination 

 planes. So capable is it of withstanding the weather, that sometimes a 

 seam of this variety forms a cliff on the hill-side, or obstruction in a 

 river bed, from which the associated shale and sandstone have more or 

 less weathered away. It is fresh and unweathered on faces that have 

 been exposed for ages. No difference is apparent between a piece broken 

 from the surface and one taken from the interior. It can be quarried in 

 large blocks, which are firm and hard, and which can be stored for an 

 indefinite time without injury. Thus, in the Saffrai valley, near the site 

 of the 'coal mine' marked on Thornton's map (1839-42), there is an old 

 moss-covered heap containing several tons of coal in blocks averaging 

 perhaps a cubic foot in bulk. The natives say it has been there years 

 and years, but none can say how long. One middle-aged man told me 

 that, when a boy, he had once gone to the place fishing, and had found 

 the heap just as it is at present, covered with moss and ferns. There is 

 a tradition that a European left the coal there, and I think there can be 

 little doubt that it is some of that raised by Mr. Bruce in 1828. Yet, 

 after nearly 50 years' exposure to the weather, the lumps are as hard as if 

 newly taken from the quarry : the fracture is rather duller, or less 

 lustrous, than that of freshly-hewn coal, but that is all the difference 

 discernible. 



Sometimes the hard coals display on the broken face a rather 

 small c^boidal fracture, the sides of the cuboids being parallel and perpen- 

 dicular to the plane of bedding. This variety is somewhat more tender 



( 3i6 ) 



