G. H. Kinahan — Geology of Parts of Galway and Mayo. 461 



A summary of the facts collected while examining this district 

 would seem to lead to the following conclusions : — 



First — The oldest rocks, which seem to be of Cambro-Silurian age, 

 wer« deposited and acquired a thickness of many thousand feet; and 

 during their deposition, but especially while the rocks in Groups 

 /S^" and /3'^ were accumulating, vulcanicity was at work, — rocks, both 

 molten and in the form of tuff, being ejected from great fissures. 

 The ejected materials formed extensive bed-like masses interstratified 

 with the sedimentary rocks, while the portions that remained in the 

 fissures now appear as dykes and intrusions among the lower beds. 



Second. — The Cambro-Silurian rocks were crumpled, contorted, 

 broken up and displaced, while their mineral conditions were changed ; 

 all the beds being more or less metamorphosed, some even graduat- 

 ing into granite. After these rocks were metamorphosed, there were 

 intrusions of other granites. 



Third. — A denudation that removed nearly all those parts of the 

 Cambro-Silurian rocks that were unaltered, and a considerable portion 

 of the metamorphic rocks, so that in some places the completely altered 

 rocks (granite) were exposed ; this is proved by the Upper Silurian 

 conglomerates containing numerous blocks and fragments of the 

 granite. The denudation must have been accompanied by a rising of 

 the land. 



Fourth. — A depression of the land, during which the Upper 

 Silurian rocks were deposited. In this epoch there is also proof of 

 vulcanicity, as, interstratified with the Lough Muck and Mweelrea 

 beds (l)^^-' and 6*), there are masses of tuffs and igneous rocks, asso- 

 ciated with dykes and protrusions of granite and other Ingenite rocks. 



Fifth. — An elevation of the land accompanied by denudation. 

 This must have been going on for a vast length of time, as over large 

 areas all the Upper Silurian rocks were denuded away, and probably 

 portions of the Cambro-Silurian and the Granite, prior to any of the 

 Carboniferous rocks being deposited, as the latter rocks rest not only 

 on the upturned denuded edges of the Upper Silurian rocks, but often 

 overla,p them, and are found deposited on the granite and other 

 hypogene rocks. Moreover, it apjDcars probable that the denudation 

 of the older rocks had almost ceased in this area when the Carbon- 

 iferous rocks were deposited, as in only a few places, and these of 

 small thickness, do arenaceous or argillaceous rocks intervene between 

 the denuded rocks and the Carboniferous Limestone. 



Sixth. — A depression of the land during the deposition of the 

 Carboniferous rocks. 



Seventh. — An elevation of the land while the Carboniferous rocks 

 were denuded. 



Eighth. — A vast time between the end of the Carboniferous period 

 and the dawn of the Glacial, in which the events that happened are 

 unrecoi'ded. Newer rocks may have once covered the area ; but if 

 they did, they seem subsequently to have been removed, as no positive 

 traces of them can be found in the Glacial accumulations.^ 



1 In one locality, Ballycurrin, on the east of Lough Corrib, a block of fibrous 

 gypsum was found in the drift. This possibly may be a record of newer formations 

 than the Carboniferous. 



