BRITISH ASSOCIATION MEETING. 



537 



tions. In some parts there were broken bands of coal, thrown about in an 

 extraordinary way. The whole of the highly-inclined strata were surmounted 

 by new red sandstone. It was remarkable that there was in this cutting an 

 enormous amount of calcareous and other grit, some bodies of which might be 

 s-upposed to have formed a regular part of the mountain-limestone. There 

 were also large masses of red substance, evidently formed by concretion, 



ON THE GRANITE-ROCKS OF DONEGAL AND THE MINERALS 

 ASSOCIATED THEREWITH. 



By R. H. Scott, Esq. 



The author gave a short account of a mineralogical tour made by him, in 

 company with Prof. Haughton, the result of which seemed to throw sor^.e 

 light on the possible origin of granite. The district visited was Donegal, 

 which county consists mainly of gneiss and mica-slate, and is traversed in a 

 north-east direction by an axis of granite. This granite is of a peculiar com- 

 position, containing two felspars, one orthose, but the other not albite, as in 

 the granite of the Mo rue mountains, but oligoclase — a mineral whose occur- 

 rence in the British Islands had only been noticed within the last twelve 

 months. Prof. Haughton, to whom this discovery is due, was unfortunately 

 unable to attend the meeting. The facts were briefly these : — The granite 

 contains oligoclase and quartz, which combination appears to be a proof that 

 the rock never was in a melted condition ; as in that case these two minerals 

 would have acted on each other and formed common felspar. It lies in beds 

 corresponding to the general lie of the strata of the country, and in its cha- 

 racter is essentially gneissose ; and, lastly, at points inside the area of the 

 granite, metamorphic rocks (limestone and slates) are found with their bedding, 

 which is nearly vertical, unchanged. These bands run for a distance in one 

 case of nine miles across the country. The condition of these rocks is very 

 similar to that of the same rocks outside the granite area ; and it is a point of 

 great interest to determine how they got there. The solution of this offered 

 by the author of the paper was that the whole of the rocks had been originally 

 stratified, and had been subjected to some actions which had been termed 

 metamorphic. The result ot such action was to convert some into granite, 

 some into gneiss, and some into crystalline limestone and mica-schist, without 

 very much altering their relative positions. The possibility of granite being 

 produced by other means than simple heat seemed to them to be proved by 

 the occurrence of felspar in quartz-veins, which are usually admitted to have 

 been filled by means of infiltration. There were several points in connection 

 with these granites which showed a close relal ion between them and the gra- 

 nites of Norway. The whole question required a careful chemical and miner- 

 alogical examination, which could not be concluded for some time. Among 

 the types of rock found in Donegal is a syenite, the felspar of which is oligo- 

 clase. The origin of this rock the author is disposed to attribute to the addi- 

 tion of limestone to the granite. A similar syenite occurs at Carlingford, but 

 contains anorthite, a felspar which would result from the admixture of a larger 

 quantity of limestone than is necessary to produce oligoclase, and has been 

 proved by Prof. Haughton to have such an origin. The anorthite-i-yenite never 

 occurs unless limestone is present in large excess, which is not the case in 

 Donegal. The district described is very rich in minerals, some extremely rare. 



VOL IV. 



