360 SKY. GEOLOGY. COAL. 



between the Lydian stone and that rock will appear 

 conspicuous, and we have only to consider it as a shale 

 brought into the state of basalt by fusion, without such 

 further disturbance as to destroy its original stratification. 



Although both the neighbouring sandstone and alternat- 

 ing shale which have undergone no change from the vicinity 

 of the trap, contain shells, and that they occur in other 

 places in the indurated strata, there are no marks of 

 them in this bed of Lydian stone. They may nevertheless 

 exist, although they escaped my observation. There is 

 little doubt that the instances of basalt containing shells 

 which have so often been described, have been cases 

 analogous to this : the observers, attending to the com- 

 position rather than to the disposition of the rock, having 

 easily been led into error from the perfect similarity 

 of the indurated shale to fine grained basalt. 



Before terminating these remarks on siliceous schist 

 I must notice a circumstance apparently of an analogous 

 nature, but the rock being unconnected with any other 

 strata capable of indicating its natural affinity, could 

 not be referred to its proper place in the preceding 

 description. It consists in some beds of quartz that 

 occur in the hill of Greaulan near the northern part 

 of Trotternish. Similar beds have been mentioned in 

 describing Strath, and it is probable that the present 

 owe their origin, like those, to sandstone strata thus al- 

 tered by the influence of the superincumbent trap ; a change 

 similar to that which occurs in the strata at Duntulm, 



There is but little to be said respecting the coal of 

 Sky, the position of this mineral being commonly as 

 obscure as its quantity is insignificant. Although a 

 subject of much anxiety to the inhabitants and pro- 

 prietors, it presents but little to reward the toil of a 

 geologist. 



It is found in two distinct positions, in the one case 

 included in trap, in the other interposed among the 

 upper strata already described. 



