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 ina 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 
