G. R. Kinahan — Possible Irish Laurentian MocJiS. 427 



ground is so broken and contorted, almost every rood, in critical 

 sections and areas, must be hammered over. Grave error may lurk 

 in any overlooked fault or reversal. It sometimes takes weeks of 

 hard toil to arrive at a result which may be expressed in a line. 

 Facts, seemingly conflicting, keep the mind in discouraging per- 

 plexity, till one more blow of the hammer strikes out a spark which 

 illuminates the seeming chaos, and reveals the harmony of the 

 whole. Patient work will hardly fail to unearth new truths even 

 in the most battered and metamorphosed patches of the crust. The 

 results to be obtained are surely neither uninteresting nor unimpor- 

 tant. As the astronomer, by inventing new instruments, penetrates 

 more deeply into the remote abysses of stellar space, and resolves 

 dim nebulae into groups of suns; so the Archgean geologist strives 

 to reach further and further back towards the beginnings of the 

 earth, and refuses to accept a barrier to his further investigations. 



VII. — Possible Laurentian Eocks in Ireland. 

 By G. H. Kinahan, M.R.I.A., etc. 



AS the Arch^an geologists have turned their attention to the Old 

 Irish rocks, perhaps it may be allowable to give a short 

 description of them. 



This school of geologists from their published papers would seem 

 to lay great stress on lithological characters ; while to me it would 

 appear that Petrology, or the stratigraphical position of rocks or 

 rock masses, was more important. Some of the changes found in 

 rocks, that geologists suppose to be petrologically the same, they 

 state are quite impossible by chemical laws ; but as such changes are 

 quite palpable to field geologists, I would suggest that possibly the 

 Chemist is acquainted with some laws to them unknown. 



The Irish rocks that have been suggested to be of Pre-Cambrian 

 age are metamorphic and granitic rocks in the Carnsore district, 

 S. E. Wexford; metamorphic and granitic rocks in West Galway 

 and S. W. Mayo ; gneissose rocks in Erris, N. W. Maj'-o ; metamor- 

 phic and granitic rocks in Donegal and parts of Derry and Tyrone ; 

 while rocks that will possibly be so classed are metamorphic rocks 

 in N. E. Antrim near Ballycastle. 



The rocks of the Carnsore or S.E. Wexford district I have very 

 carefully worked out, and to me it appears that northward and 

 westward they gradually merge into unmetamorphic rocks ; and 

 in the latter are found Oldhamia, a Cambrian fossil. 



The West Galway and S.W. Mayo rocks have also been carefully 

 worked out. In them there are two zones of hornbleudic and 

 pyroxenic rocks ; lithologically very similar, if not identical, with 

 the Laurentians of America and Scotland ; but at the same time 

 perhaps more like the Huronian rocks ; especially those of the 

 lower zone, as Logan's description of the Huronian rocks would 

 do for the latter. The rocks of the upper zone lie above others that 

 contain fossils which have been pronounced by Harkness, Baily, and 

 other authorities to be of Llandeilo types. In portions of the area 



