[ 151 ] 

 GEOI^OGICAIv NOTES FROM WEST GALWAY. 



THE GAI^WAY AND CI.IFDEN RAII^WAY. 

 BY ROBERT J. KIRWAN, B.A., B.E. 



In this paper I propose more particularly to describe the 

 rock sections exposed by the cuttings for the portion of the 

 new Galway and Clifden Railway lying between Oughterard 

 and Recess. The rocks cut through belong for the most part 

 to the schistose series, the origin and age of which have long 

 been involved in doubt. The officers of the Geological Sur- 

 vey, who first examined and mapped this district, believed 

 these schists to be metamorphosed sedimentary rocks of 

 Cambrian age, while some geologists believed them to be 

 Pre-cambrian ; and the overlying quartzites were supposed 

 to be Cambrian or Lower Silurian. Within the last few years 

 the Survey has carefully re-examined some parts of Conne- 

 mara, and similar areas occurring in Mayo and Donegal, with 

 the result that the older theories have been found altogether 

 untenable.' Most of the schists are proved to be igneous 

 rocks, which have been altered during successive periods of 

 metamorphism. There is, however, one notable exception. 

 The crystalline and often schistose limestones of such fre- 

 quent occurrence as bands in the schists must be the remains 

 of a sedimentary deposit, probably of Ordovician age. Later 

 still than the metamorphic periods came violent earth- 

 movements, which crushed the rocks over large areas, but 

 especially along certain well-marked lines in the neighbour- 

 hood, of which even the hard resisting quartzites have been 

 crushed into small fragments or even powdered. These 

 crushed rocks, when recemented by infiltered matter, form 

 interesting conglomerates or breccias, some of which were 

 supposed to be Carboniferous shore-beds by the surveyors. 

 Of a later age than some of these earth-movements, but older 

 than many, are the great granite outbursts which have pene- 

 trated the schists and quartzites, as veins, dykes, and intrusive 

 masses. In this district are also dykes of eurite, which may 

 be later offshoots of deeper portions of the granite, which 



* See " Report of the Director-General of the Geological Survey," 40/A 

 Rep. Depart of Science and Art ^1893^, P* 266, and ibid.^ 41^/ Report^ (x2>(^/\)^ 

 p. 270. 



