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brown, (3 with trace of red). It is associated with a brown mica. Iron 

 ore is abundant, olivine rare. The augite contains glass inclusions and 

 empty spaces which often take the form of negative crystals. This dyke 

 is very probably of Tertiary age. 



At Rostrevor, Co. Down, on the north side of Carlingford Lough, occurs 

 a uralitic diabase (proterobase). It contains, according to Professor VON 

 LASAULX, plagioclase, augite, uralite, viridite, magnetite and apatite. The 

 felspar gives lath-shaped sections. The augite varies from reddish brown to 

 colourless. It is altered at the margins into green fibrous uralite. The twin- 

 planes of the augite can be followed into the uralitic aggregates. Sections 

 approximately parallel to the clino-pinacoid of the augite give extinction 

 angles, referred to the trace of the face of composition (100), of 37 in the 

 augite and 10 in the uralite. The viridite (chlorite) is distinguished from 

 the hornblende, which it resembles in colour, by its feeble double-refraction. 

 The rock is termed a eucrite by Professor VON LASAULX. Two specimens 

 of the same type of rock from Rostrevor have been examined by the 

 present writer. Uralite is not conspicuous in either of them, quartz and 

 epidote occur in one, a feebly polarizing and feebly pleochroic chlorite in 

 both. The ophitic structure is most pronounced, and the iron-ore occurs 

 in the large ragged plates so characteristic of the older diabases. These 

 two specimens are identical in every respect with the non-olivine bearing 

 ophitic diabases of Wales, Devon and Cornwall. 



The " greenstones " of the Island of Lambay are intrusive in lower 

 Palaeozoic strata. The best known is the so-called Lambay Porphyry. 

 This rock has been described in detail by Professor VON LASAULX. 

 Macroscopically it consists of conspicuous plagioclase crystals, now 

 generally of a pale greenish tint, embedded in a dark green compact 

 matrix. The porphyritic plagioclase crystals are as a rule so much 

 altered that the twin striation is unrecognizable. 



The ground-mass of the rock contains, according to VON LASAULX, 

 minute lath-shaped felspars, viridite, epidote, sphene, leucoxene, magnetite, 

 pyrite and calcite. Viridite (chlorite) is the most prominent constituent. 

 In some cases augite may be distinctly recognized and its relation to the 

 viridite is such as to show that the latter mineral must be regarded as its 

 alteration product. The general alteration to which the rock has been 

 subjected makes it difficult to say whether any interstitial matter originally 

 existed. The rock is termed diabase-porphyrite by VON LASAULX and 

 ROSENBUSCH. 



Basic igneous rocks occur in the Lower Palaeozoic region of Wicklow, 

 Wexford and Waterford. Some of these are perfectly typical ophitic 

 diabases (dolerites with chlorite, epidote, leucoxene, and other alteration 

 products) with large skeletons of titaniferous iron-ore. They exactly 

 resemble the corresponding rocks of North Wales, Devon and East Cornwall. 

 Good examples of this type occur at Rathdrum, Co. Wicklow, Tintern 

 Bridge, Co. Wexford, and near the town of Waterford. Professor VON 

 LASAULX mentions the occurrence of a diorite about half-way between 

 Rathdrum and Avondale Castle. The rock shows rough columnar jointing 



