KiNAHAN — On Supposed Upper Cambrian Roeks. 343 



LYI. — Supposed Upper Cambrian Eocks in the Cotjnties of Tyrone 

 AND Mayo. By G. H. Kinahan, M.R.I. A., &c. 



[Eead, December 8, 1879.] 



During the examination of tlie Fintona and Curlew Mountain districts, 

 for the purpose of preparing the Report to the Academy thereon, the 

 wild hilly tract of metamorphosed rocks extending from a little south 

 of Cookstown westward towards Omagh was explored. In this area 

 some of the more notable hills are Craigballyharky, Craigardhessiagh, 

 Grarragrim, Creggaunconroe, Carrickmore, &c. Reasons will now he 

 given for believing that the metamorphic rocks of this district are of 

 Cambrian age. 



Let us first consider their stratigraphical position. This will be 

 best determined, if it can be determined, by their apparent relations 

 with the fossiliferous rocks of the small district at Pomeroy, which, 

 from their fossils, are generally regarded, and with good reason, as 

 Cambro-Silurian ; though this cannot be said to be absolutely proved 

 (they may well be of similar age to the English Caradoc). The 

 principal points in favour of this conclusion are their similarity to the 

 fossiliferous rocks which, at Lisbellaw, in the Co. Fermanagh, are 

 undoubtedly covered unconformably by the red arenaceous Silurian 

 rocks (Dingle grits). Moreover, in the low country a little north of 

 Creggaunconroe, the numerous large angular blocks of the arenaceous 

 red Silurian rocks seem to be nearly m situ, which would suggest that 

 an outlier of these rocks rests directly on the metamorphic rocks. 

 It has been suggested that these blocks have been carried northward 

 to their present site by ice ; but the weight of evidence seems to be 

 against such a supposition. First, the shapes of the bosses of rock in 

 the hills northward of Pomeroy seem to indicate that the ice was going 

 southward ; secondly, the drift of the country south of these hills is 

 largely made up of the debris of these rocks ; and thirdly, no large 

 blocks of these arenaceous red Silurian rocks are found in the country 

 between this assemblage of blocks and what are evidently their parent 

 rocks near Pomeroy. This, however, although suggestive, is not of 

 great weight; for if the ancient metamorphic rocks were hills in the 

 Silurian sea, arenaceous deposits may have accumulated on one side, 

 and argillaceous on the other. The age of these Pomeroy fossiliferous 

 rocks is a subject that I hope to enter into more fully at a future 

 time. 



These altered eruptive and sedimentary rocks are undoubtedly of 

 much greater age than the overlying fossiliferous Pomeroy rocks ; as 

 they were contorted, ruptured, upheaved, metamorphosed, and de- 

 nuded prior to the latter accumulating on and against them. If the 



