350 SKY. GEOLOGY. SECONDARY STRATA. 



are much more generally granular than compact, and 

 some of them indeed formed of an aggregate of rounded 

 grains of the size of mustard seeds ; not much differing 

 from some of the oolites, but more compacted, and 

 generally containing, besides these grains, crystallized 

 platy particles. These strata are intersected in a re- 

 markable manner by trap veins ;* but I shall defer the 

 consideration of those to their proper place, the last in 

 the history of the rocks. 



Reasons will hereafter be produced for supposing that 

 these veins proceed from the great masses of trap which 

 cover all the .northern portions of this promontory ; and 

 these circumstances may perhaps assist in explaining the 

 differences in character between the strata of this shore 

 and those of Swishnish opposite to it. The examination 

 of the southern and western shores of Strathaird itself 

 will show that similar differences exist among these strata, 

 even where they lie near each other and admit of being 

 continuously traced. On the eastern side of the pro- 

 montory and towards its southern extremity, the trap 

 veins diminish gradually in frequency till they nearly 

 vanish altogether, and about the same place the incum- 

 bent trap also ceases. Here the sandstone is found with 

 its most ordinary characters, tender in texture, often 

 calcareous, and generally white, but sometimes grey or 

 brown so as not to be distinguished from that of Swish- 

 nish. It occurs in the same form on the western shore 

 of the promontory, where no trap exists ; and it here 

 possesses the same complicated schistose structure as the 

 hard strata ; but more perfectly, inasmuch as the laminae 

 actually separate to a considerable depth by the action 

 of the weather. If the dips of the strata on both shores 

 are now compared, it will be seen that the same bed 

 which is hard in one place is soft in another ; this differ- 

 ence being regulated by the presence or absence of trap. 



* Plate XVI. fig. 1; 



