Yol. 65.] ROCKS OF THE TOTTRJJAKEADY DISTRICT. 137 



Mount Parfcry neighbourhood differ in several respects from those just 

 described and are far more variable. One (133) has many vesicles 

 filled with calcite and chlorite, and contains abundant magnetite 

 very uniformly distributed in small grains. Another from Mount 

 Partry (95) shows abundant highly-altered phenocrysts of both 

 augite and plagioclase, together with numerous chlorite-filled vesicles, 

 embedded in a ground-mass in which little can be recognized with 

 certainty. Another rock (215) from north-west of the Monastery 

 is somewhat similar, showing large highly-altered augite-phenocrysts 

 and little that is recognizable in the ground-mass ; but, in addition 

 to the augite, there are numerous pseudomorphs in chlorite after a 

 rhombic pyroxene, this mineral and the augite being often inter- 

 grown. ]S~o felspar-phenocrysts and no vesicles occur in this rock. 

 3. The rocks exposed at several points south-east of the triangular 

 area of Arenig Beds 1 mile west-south-west of Drumcoggy Rectory 

 are somewhat intermediate in character between dolcrites and 

 andesites. The low specific gravity, however, 2-75 of (140), shows 

 that they are best classed with the latter rocks. They are fine- 

 grained, rather pale rocks, and as a rule highly vesicular, the vesicles 

 being filled with calcite and chlorite. In section the felspars are 

 seen to be fairly fresh, but the augites are in the main replaced by 

 epidote and chlorite. Leucoxenized ilmenite is plentiful. 



(c) The Hornblende-Lamprophyres and Dolerites. 



Hornblende-lamprophyres. — These are all dark, rather 

 coarse-grained rocks, showing, as a rule, little in a hand-specimen 

 except hornblende. Felspars are, however, to be seen in some 

 varieties of the rock (21) from north of Gortanalderg. This rock 

 has a specific gravity of 2-89. In section hornblende is in each 

 case by far the most prominent mineral, occurring in pale-green, 

 slightly pleochroic crystals, which are often idiomorphic (see PI. V, 

 fig. 2) and frequently show the normal cleavage. Very little felspar 

 can be detected, the most prominent minerals next to the hornblende 

 being secondary quartz and a pale-green, almost isotropic, chloritic 

 mineral. Apatite is fairly abundant in (168), the rock from the 

 triangular patch of Arenig Beds west-south-west of Drumcoggy 

 Bectory, and a good deal of epidote aud calcite is present. 



Dolerites. — Those from the neighbourhood of Srah, and that 

 from a quarter of a mile west-north-west of Gortbunacullin (78) (see 

 PI. V, fig. 3), are all dark heavy rocks of medium grain, greatly 

 resembling some of those from the English Midlands. In section 

 the freshest of the rocks from near Srah (86 & 136) and that from a 

 quarter of a mile west-north-west of Gortbunacullin are seen to be 

 very similar ; they are noncrystalline, and are composed of laths 

 of labradorite, between which are wedged grains of augite, olivine, 

 and magnetite. The specific gravity of one of the rocks (86) from 

 the lower part of Stream G, half a mile north-north-west of Srah 

 Bridge, is 2-92. 



