236 



THE CARBONIFEROUS SYSTEM. 



down the south side of the arch along a line coinciding in part of its 

 course with the highly inclined underside of the coal at the north side 

 of the arch ; and (3.) Removal of the upper part of the north side of 

 the arch by denudation. Fig. 67 represents the appearances which 

 would thus be produced, and it will be seen that they very closely 

 correspond with the present condition of the deposit, not excepting its 



thinning toward the surface. If this 



Fig. 67. — Ideal representation of tJie 

 Cause of the appearances at Albert 

 Mine. 





be the true explanation, it is probable 

 that the sunken south side of the bed 

 has not yet been reached in the ex- 

 cavations. It might, however, in 

 approaching it from above, show a 

 succession of wedge-shaped included 

 masses of rock or "horses," one of 

 'which I saw in the floor of the lowest 

 level. On this view, also, the ' Jog ' 

 or fault above described may be a lateral bend received by the bed 

 in the original contortion of the strata ; and at this point the. straight 

 fracture, producing the supposed downthrow, may have left the bed, 

 and thus caused the appearance of the vein running in the former 

 course of the bed along the line of fault, and also the greater regularity 

 of the bed beyond the 'Jog.' This explanation is represented in 

 Fig. 68." 



As many readers of this work 

 may be interested in the controver- 

 sies respecting this mineral, I may 

 shortly mention its physical and 

 chemical properties, and the results 

 at which I have arrived respecting 

 its nature and origin. 



The substance has externally an 

 appearance not dissimilar from the 

 ordinary asphalt of commerce in its 

 purest forms ; but it is very much 

 less fusible, and differs in chemical 

 composition. Its fracture is conchoidal. Its lustre resinous and 

 splendent or shining. Its colour and the powder and streak on 

 porcelain, black ; and it is perfectly opaque. It is very brittle and 

 disposed to fly into fragments. Its hardness is 3, nearly, of Mohs' 

 scale. Its specific gravity is T08 to I'll (according to Jackson and 

 Hayes). It emits a bituminous odour, and when rubbed becomes 

 electric. In the flame of a spirit-lamp it intumesces and emits jets of 



Fig. 68.— The "Jog" at Albert Mine, 

 and its supposed relation to the line of 

 fault. 



