- The Rev. S-. Haughtorr's Notes on Mineralogy: - 51- 



probably once completely covered by a considerable thickness of 

 trap-rock, which still remains as an outlier in Sitabaldi Hill, 

 about 300 yards from the watercourse in which the pegmatite 

 dyke penetrates the gneiss. The trap-rocks of this hill are hori- - 

 zontally bedded, and interstratified with a freshwater stratum 

 containing Physa and other shells. 



It is certain, from the occurrence of such a mineral as Hun- 

 terite in the dyke penetrating the gneiss, that this dyke must be 

 regarded as a fissure filled by the action of water holding mineral 

 matter in solution under pressure and at a high temperature ; 

 and as the gneiss (10) itself contains Hunterite, it also must have 

 been to some extent subjected to the same Neptuno-Plutonic 

 agency. 



No. XI. On some Irish Dolomites of the Carboniferous age. 



Beds of dolomite limestone are found in many places in Ireland 

 stratified conformably to the ordinary crystalline limestones of 

 the carboniferous age. These dolomites are developed particu- 

 larly in the lower and in the upper portions of the carboniferous 

 limestone. The following analyses will give some idea of their 

 composition. 



No. 1. Dolomite, of a pale cream-colour, saccharoid ; forming 

 the uppermost bed of carboniferous limestone immediately under- 

 lying the coal-measure white sandstone of Belmore Mountain, 

 co. Fermanagh. Two specimens, four miles apart, analysed, 

 gave : — 



Per-centage. Atoms. 



(o) (b) (a) (b) 



Carbonate of lime . . . 61 -20 62'48 1-224 1-249 



Carbonate of magnesia . 37-80 36-30 0'900 0-864 



Silica ......... 0-20 0-28 



Peroxide of iron (probably\ ~ «~ ^.-^ 

 present as carbonate) . J 



Total . . . 99-80 99'66 



No. 2. Dolomite, of a rosy cream-colour, saccharoid, flaky, 

 and crystalline ; forming the uppermost bed of the carboniferous 

 limestone immediately underlying the coal-measure shales of 

 Raheendoran, Clogrennan Hill, co. Carlow — . 





Per-centage. 



Atoms. 



Carbonate of lime . . 



. 54-15 



1-083 



Carbonate of magnesia . 



. 43-01 



1-024 



Argil 



. 2-84 





100-00 



The occurrence of beds of dolomite, so pure as those just 



E2 



