352 SKY. GEOLOGY. SECONDARY STRATA. 



rocks are not limited to the island alone, as their pro- 

 longations can be traced with the same regularity to 

 the mainland and the adjacent islands, under no greater 

 anomalies than can be accounted for by the trap rocks 

 associated with them. 



Immediately after this series follows a deposit of which 

 limestone is the principal member. In the vicinity of 

 the regular sandstone these beds maintain a nearly im- 

 violated regularity of position; the exceptions which occur, 

 arising from a minor degree of those circumstances that 

 accompany the greater irregularities. But as they proceed 

 upwards, the regularity of this disposition becomes ma- 

 terially affected, while they undergo considerable changes 

 of structure; the outer boundary of the zone thus pre- 

 senting a very irregular line, marked by the disturbance 

 of some beds and the total deficiency of others. In 

 analogous cases, where such rocks are followed by other 

 secondary strata, they are equally regular at their upper as 

 at their lower boundaries ; these strata, here as elsewhere, 

 consisting of shale, sandstone, and calcareous rocks, and 

 the whole presenting a well-known set of natural affinities. 



Together with these regular secondary strata, there are 

 here found in many places a set of unstratified rocks, 

 reposing on them, occasionally alternating in an irregular 

 manner, and ramifying into veins of greater or less 

 magnitude. If the contact of these overlying rocks 

 with the strata be examined, it will be found that they 

 are rarely parallel except for a small space ; and that 

 instead of lying upon them in an even manner, they join 

 them obliquely or transversely, or meet them in other 

 irregular modes. With similar irregularity, portions of 

 the unstratified rocks intrude among the stratified, or 

 fragments of the latter are found insulated among the 

 former. 



Where the limestone loses its order and disappears, 

 a great mass of these unstratified rocks occurs, rising 

 into high mountains and occupying nearly all the northern 



