44 Lord Greenock on the Igneous Rocks 



must have taken place. We may therefore conclude, that all 

 these trap-rocks have undergone elevation at two distinct periods, 

 — the first when formed in a state of igneous fluidity at the bottom 

 of the sea, the second when, with the whole district in which 

 they are situated, they were lifted up to their present positions 

 in a hard and consolidated state. 



The convulsions, which must have been frequent during this 

 latter period, would doubtless have been most violent at those 

 points which had before been the principal foci of volcanic 

 energy ; and although there is no appearance in this place of the 

 igneous matter having then reached the surface, an expansion of 

 the interior fluid, while operating these changes of level, may 

 very probably have filled by injection rents or fissures in many 

 parts of the strata below, forming, in this manner, the dykes 

 which are often met with in mining operations, and occasioning 

 many of the faults and dislocations observed in those above, 

 where the cause itself is not perceptible. 



Consequently, there appear to be sufficient grounds for con- 

 sidering, that, during the first period, when the greenstone was 

 in a state of fusion, the fragments of sandstone, which are enve- 

 loped in it near the summit of the rock, were carried upwards by 

 the erupted fluid, the intense heat of which has probably, at the 

 same time, altered the nature of some of the contiguous stratified 

 rocks. But the derangement of the strata, and all the other signs 

 of disturbance seen in the section of the Castle Hill, are, in the 

 opinion of the author, to be referred to the earthquakes and 

 other commotions of the second period, after the consolidation of 

 these rocks ; for, although local circumstances may have contri- 

 buted, to a certain extent, in producing these appearances, yet, 

 when we can trace the operation of the same influence to extend 

 over a large district of country, determining its features and the 

 inclination of the strata, we may fairly conclude, that this has 

 been due to some more general cause, of which these separate 

 phenomena have only been subordinate effects ; and if it be 



