454 O. H. Kinahan — Geology of Parts of Galway and Mayo. 



in the service, as iie taxed his constitution with more work than it 

 could stand. During our work we received valuable aid from 

 Doctors King and Melville, of Queen's College, Galway, and Prof. 

 Harkness, of Cork ; also from Sir R. Griffith, Bart., the latter 

 veteran geologist, on account of his universal knowledge of the 

 geology of Ireland, having given us invaluable hints and suggestions. 

 Prior to the work of the Survey, which took seven years to com- 

 plete, this country seems only to have been consecutively examined 

 by Sir JR. Griffith. This observer studied it first about the year 

 1839, and detected fossiliferous unaltered rocks lying uncon- 

 formably on metamorphosed rocks. The first by the fossils he knew 

 to be of Upper Silurian age, while the latter he considered to 

 be of the same age as the rocks in the counties of Wicklow and 

 Wexford, in which Lower Silurian fossils were afterwards found. 

 Subsequently this country was traversed by the late Sir R. I.Murchison 

 and Prof. Harkness, both of whom from their published accounts 

 are found to consider Sir E. Griffith's suggestions correct. The 

 officers of the Geological Survey, after considerable labour, were in 

 part able to confirm this opinion, as will appear from the description 

 of the rocks. 



The newest rocks that, occur in this country are of Carboniferous 

 age. To the north Carboniferous Limestones occur in the neighbour- 

 hood of Clew Bay, and from that they extend first eastward and 

 then southward to Galway Bay, forming a boundary to the older 

 rocks. Besides this large tract, small outliers of Carboniferous 

 rocks occur in various places, consisting of sandstones, conglome- 

 rates, etc., which have been detected in various widely detached 

 places, and thereby proving that the rocks of this age once covered 

 the whole country ; while the flattish tops of some of the highest 

 hills are portions of the bottom of the ancient Carboniferous sea. 



The next rocks in descending order are of Upper Silurian age, 

 but of these there are two distinct sections in the area — one given 

 by the rocks in the N.E. portion of the country, and the other by 

 those to the S.W. 



South-west Section. North-east Section. 



Salrock heds. 5' 



,4 \ Mweelrea beds and Tourma- 



Longh Muck heds \ \ keady beds 



Interbedded felstones [ j3 Interbedded felstones. 



Gowlaun beds ) 



Unconformability. 



Unconformability, 0^'^ Doolough beds. 



Schist. 



The Mweelrea beds ¥ probably in parts represent both the Salrock 

 and Lough Muck beds, the lower portions of the Mweelrea beds being 

 of Upper Llandovery age, while the upper part is of Ludlow, 

 similar to the supposed age of the Salrock beds. They are, however, 

 so very differently constituted, that they have been separated. The 

 difference in the rocks in these sections seems to be due to the 

 country to the north-east having 'been dry land for a considerable time 

 after the country to the south was submerged and rocks were being 

 deposited in it. After the great fissure irruption, however, when 



