ON THE CONSTITUTION OF THE GRANITES OF DONEGAL. 65 
The test is a very severe one, and in order to show the degree of approxi- 
mation which has been attained by the method, we take the instance of the 
granite of Doochary Bridge, No. IX., and give the value of each constituent 
as calculated from the result given in Table VII., and as obtained by actual 
analysis of the rock. 
Composition of Granite of Doochary Bridge. 
Observed. Calculated. 
BNC Aes cst AGT aaswate casttcfere ebay svenuts (4 72°24 .,... 72:24 
PARTING e8 okay cnanc) y=) ohovoua tara bite 14°92. et phos0D 
Tron and manganese oxides .... 218 .... 1:52 
Ley 2 Oe ee ee ae Soe GS ics ary. 2°91 
SERIA ais oys, «fahaieynin sh ailt oehe #)9y 4 aie oh’ ciafiy: oy OED 
Sai. MAES OM five BPou eels dates 315) ee ae 2:89 
GEAR Ore a aoe Serene SO wo deere: 4-90 
99-99 99-99 
Hence we see that, although we may assume that a considerable proportion 
of the granites of Donegal are composed of the four minerals in question, yet 
the constitution of these minerals, when present in the mass of the rock, must 
differ slightly from that ascertained by the analysis of the larger crystals. 
In conclusion, we may state that complete series of the minerals and rocks 
described in this Report are preserved in the Geological Museums of Trinity 
College, Dublin, and of the Royal Dublin Society, the actual specimens 
which were subjected to analysis being in the first-mentioned collection. 
APPENDIX. 
The following catalogue of localities has been compiled, partly from the 
published accounts of the tours undertaken by Sir Charles Giésecke, in the 
years 1826-27, at the expense of the Royal Dublin Society, and partly from 
the results of the explorations carried out in the preparation of the preceding 
Report. Much valuable information has been derived from the gentlemen 
whose names have been already mentioned, and from an examination of spe- 
cimens collected by the late R. Townsend, Esq., C.E., who resided in the 
county for some years. 
The names of Messrs. Greg and Lettsom are given as authority for loca- 
lities given in their ‘Manual of Mineralogy,’ which we cannot otherwise 
identify. We regret to say that much reliance cannot be placed on these 
localities, as they have not been personally identified by the authors of that 
work (see under Analeime and Gypsum). 
All localities which have been identified by the British Association Com- 
mittee, in the progress of their investigations, are marked with an asterisk. 
CATALOGUE. 
Sracete ELements. 
Grapnire, Found in rolled pieces on the shore of Sheephayen, near Ards 
House; in the Burndale, Conyoy; i situ at Fintown. 
SuLpHuRets, dc. 
Garena, Has been worked in several localities, the chief of which are 
ey ; Marfagh; Ards; Fintown; Drumnacross; Kilrean; Mullanti- 
' F 
