HARKNESS THE GEOLOGY OB^ HOOK POINT. 



31 



concluding that they are the relics of that form of fern which is so 

 abundant in rocks of the same age in the county of Kilkenny — the 

 Cydopteris Eibernica 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 JuTcesii) of such a character as to lead to the inference £hat 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 in 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 in 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 and uniform in their course. 

 There is about these joints which intersect the conglomerates a 

 feature of great interest ; and this feature is not confined to the 

 country about Hook, but likewise manifests itself in 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, 



