TRANSACTIONS OP THE SECTIONS. 103 



distinction in the basalts of these geological ages ; but recent investigations by 

 Zirkel, D. Forbes, Allport, and others tend to show that there is no criterion of 

 age amongst the constituents of basalt, dolerite, or melaphyi-e ; and the presence 

 of oliyine, once supposed to be distinctive of Tertiary basalts, has been detected 

 amongst those even of Carboniferous age *. 



Age of the Older Basalt. — The geological age of these older basalts can only be 

 relatively determined. They are newer than the Lower Carboniferous rocks, which 

 they are seen to traverse at Cranfield' Point and Carlingford. Recollecting the 

 abundant evidences of contemporaneous volcanic action which the Carboniferous 

 rocks of Scotland'and portions of central England present, the authors are disposed 

 to refer these older basalts to the Upper Carboniferous period itself; and bavin o- 

 regard to the prodigious number of these dykes traversing the rocks at intervals 

 along the coast from Dundrum Bay to Carlingford Bay, they suggest the former 

 existence of one or more volcanic vents in their vicinity during later Carboniferous 

 times; such a volcanic focus as is inferred to ha^e existed in the vicinity of Car- 

 lingford by Professor Haughton f. 



SL'qiu')ice of Granite, Plutonic, and Volcanic rocks in the Mourne district. — • 

 The following may be regarded as the order of succession of these rocks with 

 their approximate ages in the district north of Carlingford Bay, all beino- more 

 recent than the age of the " Caradoc " or "Bala" beds of the Silurian epoch. 

 Commencing with the oldest, we have : — 



(«) Metamorphic gi-anite of Slieve Croob, CastleweUan, and Nevn-y. Pre- Car- 

 boniferous, therefore Palaozoic. 



(b) Older basaltic dykes of Mourne and Carlingford. U2W' Carboniferous. 



(c) Diorite Dykes. Later than the Carboniferous. 



1 1. Granite of Mourne j p ,„ 



(cI) \ 2. Felstone and porphyry dykes penetrating the granite \ ■, ^f~ '-'ar- 



( of Slieve Croob and the older basaltic dykes j "oii"erous |, 



(<') Newer Basalts of Miocene (Tertiary) age. 



Judging by the comparative scarceness of the newer Tertiary dykes in the district 

 of Mourne, the authors drew the conclusion, that it may be considered as the 

 southern limit of the region affected by the volcanic outbm-st of the Miocene period, 

 which so powerfully affected the district lying to the north-east of Ireland and 

 extending into the Inner Hebrides ; while on the other hand it was the seat of 

 active volcanic energy during an earlier period, which in all probability may be 

 identified with the Upper Carboniferous, or that of the Upper Coal-measm'es of 

 England. 



On tTie Coal-beds of Panama, in reference mainly to their Economic Importance. 



By the Eev. Dr. Hume. 



On the Silurian Hods of the Counties of Eoxhurgh and SeVcirlc. 

 By Chaeles Lapwoeth and James Wilson. 



The authors gave a short summary of what they had already accomplished on 

 the investigation of these strata, which they held fell naturally into five great divi- 

 sions in this district. These divisions they had named respectively, 



1. The Hawick Rocks, 4. Tlie Gala Group, 



2. The Selkirk Rocks, 5. The Riccarton Beds, 



3. The Moffat Series, 



after the places where they are best developed. 



* Mr. S. Allport, ' Geological Magazine,' vol. vi. p. 115. 



t Quart. Jom-u. Geo!. Soc. vol. xii. p. 193. 



X Professor Harkness suggests that the eruption of the granite of Mourne may be re- 

 ferred to the period which intervened between the depositon of the Carboniferous and 

 Permian strata, a period of great duration ; and he thinks there is a strong resemblance 

 between the granite of Mourne and that of ICirkcudbrightshire, wliich is referable to this 

 period. Against this view it is to be observed that it would bring the older basaltic dykes 

 ulose upon the heels of the Mourne granite, winch seems rather improbable. 



