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XXXIV. 



ON THE ECONOMIC GEOLOGY OF IKELAND. By G. H. 

 KINAHAN, M.E.I.A., Etc. 



[Read January 9, 1889.] 

 GENERAL SUPPLEMENT. 



[In this Supplement is given such information as has heen obtained since my several 

 Papers on this subject were published. I may, however, refer briefly to the suggestion 

 that some of the oldest Irish rocks, although not the equivalents of the Lauren- 

 tians, may nevertheless be possibly Pre-Cambrian.] 



INTRODUCTORY. 



Agnotozoic. — The improbability of any of the Irish rocks being 

 equivalents of either the Huronians or Laurentians has been already 

 suggested. It must, however, be remembered that in America 

 there is a great interval between Huronian and Primordial strata, 

 and that the " Gap rocks " have been found to exist in Maine, 

 Manitoba, and other places in America. Chamberlin has pro- 

 posed to call the time of their deposition the Agnotozoic Epoch, 

 which suggestion was adopted by the late Dr. Irving. 



The American Primordials would seem, from their fossils, to 

 be the equivalents of the Welsh Cambrians ; and the latter, up to 

 the present, are considered by most people to be a portion of the 

 same formation as the Bray Head Series. For this classification, 

 however, there does not seem any good reason, as both were classed 

 together solely because one was considered to be the oldest English 

 and the other the oldest Irish formation. But on examination it 

 is found that both lithologically and palseontologically they are 

 quite different. 



For some time it has been known that there are Pre-Cam- 

 brian rocks in Scotland, while Blake, Hicks, and others believe 

 they have proved their existence in England and Wales ; there- 

 fore the presence of Pre-Cambrian rocks in Ireland may also be 

 expected. 



