HARKNISSS THE GEOI-UGY OP UOUK POINT. 
31 
coucliuliiig tliat tbey are the relics of that form of fern which is so 
abundaut in rocks of the same age iu the county of Kilkenny — the 
Ci/clopteris Hibernica of the late Professor E. Forbes, — a fern which also 
makes its appearance among contemporaneous strata in the county of 
Berwickshire, at Prestonhaugh, near Dunse, associated with a Pterich- 
thys — one of the fossil fish so well described by the late Hugh Miller. 
In Ireland, however, this fern has no such companion in its burial. 
In Kilkenny we, however, find it associated with a bivalve-shell (the 
Anodon Jukesii) of such a character as to lead to the inference that in 
some localities fresh- water lakes exerted some influence in the produc- 
tion of these sandstones antecedent to the period of the Carboniferous 
limestones. 
These sandstones, and their associated conglomerates, bear about 
them features which indicate that they have been subjected to violent 
forces since they were deposited, and even subsequent to their consoli- 
dation. These are very beautifully marked by the phenomena known 
to geologists under the name of jointing; and these phenomena are 
nowhere better exhibited than iu the district about Hook Point. 
These joints consist of divisional planes, which in this locality are for 
the most part perpendicular, and run in nearly a north and south 
direction. These planes not only separate the masses of rock into 
distinct portions, but they also exhibit themselves iu the form of 
narrow openings, which seem to have resulted either from a rigid 
mass breaking itself up into distinct portions in consequence of great 
pressure, or from each separate portion — included between two joints 
— so shrinking as to leave intervals arranged in such a manner that 
these intervals shall be nearly constant aud uniform in their course. 
There is about these joints which intersect the conglomerates a 
feature of great intei'est ; and this feature is not confined to the 
country about Hook, but likewise manifests itself iu many other 
localities where we have jointed conglomerates. The quartz-pebbles 
which enter largely into the structure of these conglomerates, have 
been cut through by the force which-has produced these joints in such 
a manner as to exhibit regular smooth faces, as perfect and uniform 
as the faces of an apple when cut through by a knife. There are so 
many features in connexion with jointing in general, and so many 
phenomena of a complex character, that of all geological problems, 
