54 REPORT—1863. 
dykes of pitchstone, some of which are amygdaloidal, and also by veins of 
amethyst and of smoky quartz, the latter in very large crystals. No lime- 
stone has as yet been found in contact with it, nor have we been able to detect 
any non-granitic rocks within its area. 
The district to the S.E. of the town of Donegal, extending to the shore of 
Lough Erne, near Belleek, and comprising part of the county Fermanagh, con- 
sists of a gneiss which is different in texture from that of other parts of the 
county. Along its northern edge we find mica-slate, abounding with large gar- 
nets, kyanite, schorl, and in some places sphene. In another locality, Agha- 
doey, we find dark-green serpentine with garnet rock ; and the whole district 
is penetrated by numerous veins of granite referable to two distinct types :— 
A. Veins containing quartz, pink orthoclase, white mica, black mica, and 
schorl, Crystals large. 
B. Veins containing quartz, pink orthoclase, yellowish-green oligoclase, 
black mica, with garnets, molybdenite, and copper pyrites. Crystals 
. moderately large. 
As regards the probable age of the Donegal metamorphic strata, the Com- 
mittee do not wish to bring forward any statements in this Report, as we are 
of opinion that the district is too limited in extent for any safe reasoning of 
this nature to be based on its examination. It appears certain that rocks of 
the same nature occur in part of Connaught and in the west of Scotland; 
and it is to be hoped that the labours of the Irish Geological Survey in the 
one case, and of the Scotch Survey in the other, will put us in possession of 
data which they alone are in a position to ascertain, and which will finally 
determine the relation of these strata to the overlying fossiliferous rocks. 
Before we conclude this portion of our Report, we are bound to express the 
obligations of the Committee to William Harte, Esq., C.E., the county sur- 
veyor of the western district of the co. Donegal, who has been indefatigable 
in his exertions in aid of the researches which haye been carried on ; and also 
to J. Vandeleur Stewart, Esq., D.L., of Rock Hill, near Letterkenny, and to the 
Rey. Frederick Corfield, of Templecrone, from both of whom the Committee 
have derived valuable assistance. 
Chemical Constitution of the Granites. 
In investigating the chemical constitution of the granites of Donegal, we 
have analyzed fifteen specimens of granitic rocks from that county, and, in 
addition to these, we are enabled to lay before the Association the analyses 
(Nos. XVI., XVIL., Table V.) of two specimens selected from a series of Scotch 
granites, for which we are indebted to the kindness of Sir R, I. Murchison. 
These specimens were selected in consequence of their close resemblance to 
some of those which we findin Ireland. We have further analyzed some of the 
syenites, and seyeral specimens of the simple minerals found in the granites 
and the other rocks. . 
The result of most of these analyses have already been published in the course 
of last year by one of our number, Prof. Haughton, in the ‘ Quarterly Journal 
of the Geological Society of London’ (vol. xviii. p. 403), as a portion of his 
«« Experimental Researches on the Granites of Ireland.” We shall first speak 
of the individual minerals, then give the analyses of the rock-masses, and 
finally give the results of the mathematical investigation of the mineralogical 
constitution of the granites. ; 
Minerals of the Granite of Donegal. 
The minerals of the granite of Donegal may be divided into Constituent 
-and Accidental Minerals. 
