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' III. 



A NEW EEADING OF THE DONEGAL EOCKS.^ By G. H. 

 KINAHAN, M.E.I. A., &c. Plates I. to VI. 



[Eead November 19, 1890.] 



Introduction. 



In the winter of 1883-84 the late Gerrard A. Kinahan spent 

 some weeks in exploring the hill-country between Loughs Salt 

 and Finn, in the barony of Kilmacrenan, Co. Donegal ; and from 

 the relations of the rocks he was led to believe that a tract of 

 younger roclis^ running north-eastwards from Glen Swilly to the 

 valley of the Leannaw, lay unconformably on older, its south- 

 eastern being more conspicuous than its north-western boundary, 

 the latter being more or less obscured by drift and bog. At the 

 time my health prevented me from investigating the subject, while 

 subsequently my duties required that I should more especially 

 examine the country near Lough Swilly. But during the year 

 1885 my examination of the rooks in that country led me to believe 

 that my son's conclusions were right, while more extended research 

 in subsequent years has more fully confirmed them. 



From the memoirs and map recently published by the Geo- 

 logical Survey,^ it is evident that Dr. Geikie and the officers 

 working under him have been under a misapprehension similar to 

 that of the earlier surveyors of the country in the neighbourhood of 

 Lake Superior. These American explorers supposed that the grits 



1 This Paper was originally written in 1886 ; it lias since been revised, and addi- 

 tional facts added in confirmation of the original theory. The original Paper was not 

 read as the Director-General of the Geological Survey considered that it was premature, 

 and therefore would not give the required sanction. 



2 In one of these memoirs the writer's name appears ; but his description of the 

 rocks of a portion of the Barony of Kilmacrenan has been in places so modified by the 

 official editor that the writer cannot be held responsible for the present representation 

 of it. 



