102 Proceedings of the Royal Irish Acadeniij. 



XVII. — Geanitic aij^d other Iistgeis'ite Eoces of Tae-Connaitght, and 

 THE Lower Owle ; oe the mountainous teact oe countet ayest oe 

 Loughs !Mase: and Coeeib. By G. Heney Kinahan, M. E. I. A., 

 r. E. G. S. I., &c., with Plates 9, 10, 11 and 12. 



[Eead November 13, 1871].* 



Object of the Essay. 



During an examination extending over seven years on the part of 

 the Irish branch of the Geological Survey of the United Kingdom, 

 of the rocks in the mountainous country west of Loughs Mask and 

 Conib (parts of the counties Mayo and Galway), certain facts as to 

 their age, position, and relations to one another were gradually 

 developed, and certain convictions as to their origin formed. 



In this paper it is proposed to lay before the Academy an epitome 

 of the facts observed ;f also some suggestions in regard to the origin of 

 the granites and other ingenite rocks. | 



The latter are sj^ecially put forward in the hope that they may be 

 examined and criticised by more competent judges than the author, and 

 thereby their value proved. 



In the first part of the paper it is proposed to enumerate and give 

 a general description of the rocks ; while in the second part will be 

 found suggestions to account for their origin and relations one to the 

 other. 



* The publication of this paper has unavoidably been delayed by the MSS. 

 having been mislaid after it was referred to Council for publication. 



t The details relating to these rocks will be found in the published memoirs of 

 the Irish branch of the Geological Survej\ 



\ Mr. D. Forbes has proposed to divide all rocks into two great classes. First, 

 Ingenite rocks (born, bred, or created within or below) ; and second, Derivate rocks, 

 " since dii'ectly or indirectly they are all derived from the destruction of the former." 

 (The Microscope in Geology, by David Forbes, F. R. S., page 6), reprinted from 

 the PopuLxVR Science Review, October, 1867. In the fii-st are included all 

 granitic, metamoi-phic and igneous rocks, while the second contains all sedimentary 

 and other subaqueous or subaerial accumulations. The geological terms neces- 

 sary for a description of the ingenite rocks have been used by some authors in 

 most conflicting senses, while many rock-names are unintelligible on account of 

 their being given by the many writers to rocks of different characters. In this 

 essay all words of one class wUl have the same signification. Thus, words ending 

 in ic or ose, will signify ' belonging to' ; as. Granitic, belonging to granite ; Schistose, 

 belonging to schist ; and words ending in old will signify ' like ' ; as granitoid, 

 granite-lxke ; gnelssold, gneiss-like, &c. Eock-names, except when absolutely 

 objectionable, will be used for the rocks to which they were originally given, but at 

 the same time, to prevent confusion, the ordinary composition of the rock will be 

 stated. Dana's suggestion for an ending of yte instead of Ite for rock-names wiU 

 be adopted, also his name for minerals. 



