1817.] to the Giant's Causeway. 123 
cavity while the rock is im situ. Moreover, the surface of the cal- 
cedony or opal next to the empty space is always found to be flat and 
horizontal, which would show that the substance must have been 
filtered into its situation in a fluid state, and afterwards consoli- 
dated. 
When I left Belfast for the Giant’s Causeway, it was my intention 
to have proceeded on to Ballycastle and Fairhead, where I under- 
stand is an ample field of most interesting investigation for the 
mineralogist. Dr. M‘Donnell, of Belfast, informs me that on the 
east side of the latter place we have coal and basalt within a quarter 
of a mile of a primitive rock mica slate. From the above gentle- 
man, to whom I had the good fortune to be introduced, I received 
the most polite and kind attention, and very ample information 
with respect to the geognostic appearances to be observed at the 
Giant’s Causeway, and round the coast road. But as my time was 
limited, 1 was under the necessity of reluctantly abandoning m 
intention of visiting Fairhead, and of returning to Belfast by the 
way in which I had come. Dr. M‘Donnell bas a large and interest- 
ing collection, well worth seeing. 
On returning to Gatehouse of Fleet, and being called by business 
to the shore of the Solway Firth at Airds and Balcarry, situated on 
a portion of the Galloway transition country, nine miles to the 
south-west of Kirkcudbright, 1 took the opportunity of examining 
a few miles of the bold rocky coast there. It is sufficiently inte- 
resting. Here within a mile of one another we have the granite, 
the transition rocks, and the old red sand-stone. 1 observed the 
granite of the Criffle district within a mile of Balcarry House 
seemingly very near the greywacke, but could nowhere see a junc~ 
tion. On the seashore in the Creek half a mile to the south-east 
of Balcarry House, opposite the Isle of Heston, is a granite vein 
of about LO inches thick in a rock quite similar-to the compact or 
fine-grained gneiss of the Lauran. This vein cannot be traced to 
the granite rock, On walking about a mile further round this shore 
to the westward, in company with Mr. Brown, Land Surveyor, 
along tremendously high cliffs of greywacke and greywacke-slate 
(the strata very highly inclined, and in the usual direction), we came 
upon an interesting and very distinct junction of the above rocks 
with the old red sand-stone. This junction is completely exposed 
by the sea, and affords a fine opportunity of observing on a large 
scale the influence of the one formation on the other. The transi- 
tion strata (slate) are elevated about 70°, and dip towards the sand- 
stone, the strata of which are conformable in position. For 15 or 
20 yards you can see the one rock affecting the other; that is to say, 
at about the above distance from the pure slate, the sand-stone be- 
comes evidently penetrated by the slaty matter, and continues more 
and more so as we advance, until it ends in pure slate. Half way 
between them is a substance which is neither the one nor the other, 
but a /erlium guid formed of thetwo. In short, the passage of the 
transition and floetz rocks into one another is here very striking. 
