XVIIL—ON THE LAURENTIAN ROCKS OF DONEGAL, AND OF OTHER 
PARTS OF IRELAND. By Epwarp Hott, LL.D., F.R.S., &c., Director 
OF THE GEOLOGICAL SuRVEY OF IRELAND. Puares XX. anp XXI. 
[Read 21st November, 1881.] 
INTRODUCTORY. 
The following is an account of the more important papers dealing with the 
formations of Donegal, which constitute the chief topic of the present paper :— 
Mr. Robert H. Scott, F.R.S., in a paper “ On the Granitic Rocks of Donegal,”*® 
describes the three granite districts represented on Griffith’s Geological Map—that 
of Barnesmore, of Ardara, and of the large tract ranging. from Lettermacward to 
Glen, along the valleys of the Gweebara and Glenveagh rivers. The examination, 
in which he was assisted by the Rey. Professor Haughton, was restricted to the 
south-western portion of the county. He states his opinion that “the typical 
Donegal granite,” as a whole, “ presents no appearance of being a purely igneous 
rock, the evidence, in fact, pointing to a metamorphic origin for it.” Again he says, 
“it is thoroughly gneissose in its character, and lies in thin beds corresponding to 
the bedding of the stratified rocks of the country.” 
Mr. Ethelstone H. Blake, in a paper “On the Primary Rocks of Donegal,”+ 
describes sections of the granitic and associated rocks, which he considers assume 
almost everywhere a vertical position. He agrees with Mr. Scott in considering 
the Donegal granite not to be of igneous origin. 
Mr. R. H. Scott, ina paper ‘‘ On the Granitic Rocks of Donegal, and the minerals 
therewith associated,” being a continuation of his former communication, gives an 
account of observations made during a tour, in company with Mr. Rk. Byron, in the 
south and west of the county, and afterwards with Professor Jukes; he also 
acknowledges his obligations to Mr. Harte, County Surveyor. He considers the | 
igneous rocks of Inishowen to be undoubtedly contemporaneous with the sedimen- 
tary rocks of the district, and appeals to the sections along the coast between Bun- 
crana and Carndonagh. ‘The typical granite is everywhere stratified with an east- 
ward dip, and becomes more gneissose as you approach the edge of the district. 
A very complete catalogue of the minerals of county Donegal and their localities 
is appended. 
* Journal Geol. Soc. Dublin. Vol. IX., pp. 285-294. + Journal Geol. Soc. Dublin. Vol. IX. p. 295. 
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