188 Scientific Proceedings, Royal Dublin Society. 



(9) Blake, Eev. J. P. : 



" Report on the Microscopic Structure of the Older .Rocks of 

 Anglesey."— Rep. Brit. Assoc, Bath, 1888, p. 367. 



(10) Blake, Rev. J. P. : 



'■'■ On the Monian System of Rocks." — Quart. Joum. Geol. Soc, 

 London, vol. xliv., 1888, pp. 475, 534. 



(11) Memoirs of the Geological Survey, 102 and 103 ; 112, p. 37 : 1875 ; 



121 and 130, p. 4 : 1869. 



(12) BoNiTEY, Rev T. G. : 



"JS'ote on some Pebbles in the Basal Conglomerate of the Cam- 

 brian at St. Davids," — Geol. Mag., Dec. 3, vol. vi., p. 315. 

 1889. 



EXPLANATION OP PLATE XV. 



Pigs. 1 and 2. — Micro-photograph from a thia slice of quartzite 

 from Carrickgologan — fig. 2, as seen with ordinary light; fig. 1, between 

 crossed jSTicols. The black spot on the right of fig. 2 is a cavity where 

 the quartzite has been torn away in grinding the slice ; it can be identified 

 on the left of fig. 1. By turning one of the figures through 180° in the 

 plane of the paper, it will assume the position of the other, and the 

 difference in appearance of the several constituent grains produced by 

 crossing the Nicols can then be clearly traced. 



Pig. 3. — Micro-photograph from a slice of garnet-bearing mica-schist 

 from Glendalough. Near the centre of the field is a fragment of garnet 

 which has been torn away from a crystal-aggregate on the left during 

 post-Ordovician earth movements. It is traversed by fractures, seen as 

 dark lines crossing it from side to side, and these are continued through 

 the surrounding quartz as planes of vapour cavities. 



Pig. 4. — Photograph of a bed of quartzite near "The Cave" on the 

 Sutton side of Howth, showing numerous parallel quartz veins. The 

 scale cannot be fairly judged by the figure sitting in the left hand upper 

 corner, as the photograph was taken by a very short-focussed lens. 



Pig, 5, — Photograph of a fragment of quartzite and slate, about one- 

 third natural size. The quartzite at the top of the figure is traversed by 

 numerous open cracks having their planes perpendicular to the cleavage 

 planes of the slate seen below. 



