134 



may therefore be conveniently designated olivine-diorites. T ho latter stand in 

 close relation with the rocks described by Professor BONNEY as hornblende- 

 picrites. 



Corsitc. This name, originally applied to the orbicular-diorite of 

 Corsica, also called Napoleonite, is used by ZIRKEL for any variety of 

 diorite in which the felspar is anorthite or some allied species. 



Eucrite. This name was introduced by Gr. ROSE. It was subsequently 

 limited by ZIRKEL 1) to a compound of anorthite and augite. Such a rock 

 consisting of 62 per cent of anorthite and 38 per cent of augite, has been 

 described by Dr. HAUGHTON (2) as occurring in the Carlingford district, Ireland. 

 Yon LASAULX describes a rock occurring at Rostrevor, County Down, as a 

 eucrite. (3) It consists of plagioclase (labradorite or anorthite), augite, uralite, 

 viridite, magnetite and apatite. 



Augite-dioritc. ZIRKEL proposed this name for oligoclase-augite rocks. 

 Mr. COLE (4) has recently suggested that it should be used without reference 

 to the character of the plagioclase. 



Diabase. This term was introduced by A. BROGNIART (5) for rocks which 

 would now be termed diorite. HAUSMANN proposed in 1842 to revive the 

 term, which had been dropped by the consent of its author, for rocks containing 

 hypersthene [augite], labradorite and chlorite. (6) ZIRKEL defines diabase as a 

 rock consisting of labradorite, augite and chlorite. ROSEN BUSCH employs the 

 term (7) for a pre-tertiary holo-crystalline massive rock composed essentially 

 of plagioclase and augite. He does not recognise chlorite as an essential 

 constituent, because it can be shown to arise in consequence of the alteration of 

 augite and to be, therefore, a secondary and not an original constituent. He 

 divides the diabases into two groups ; diabase proper and olivine-diabase. If 

 we disregard geological age, then ROSENBUSCH'S diabase corresponds very 

 closely with our dolerite ; the only difference being that the term dolerite does 

 not abolutely exclude the presence of a small amount of interstitial matter. 



Diabase-jjorphi/rite, La bmdo rite-porphyry and Porphyritio-dolerifa. These 

 terms are employed for certain representatives of the basic magma in which 

 porphyritic crystals of labradorite, bytownite or anorthite occur in a dark, 

 fine grained or compact groundmass. The two former are employed on the 

 Continent for pre-tertiary rocks. Professor JUDU has shown that precisely 

 similar rocks of tertiary age occur on the west of Scotland. 



Augite-porphyry. Name applied to a rock containing large crystals of 

 augite. Such a rock occurs as a dyke at Crawfordjohn in Lanarkshire. 



Variolite. A name applied by French petrographers to a compact variety 

 of diabase, characterised by light circular spots on a dark groundmass. The 

 variolitic structure occurs at the margins of certain masses of normal diabase 

 (plagioclase-augite-chlorite rock), and is therefore a contact phenomenon. 



(1) Lehrbuch der Petrographie, 1866. Vol. II., p. 135. 



(-2) Q.J.G.S. Vol. XII., 1856. p. 197. 



(3) T.M.M., Neue Folge. Vol. 1. p. 433. 



(4) G.M. Decade III. Vol. III. p. 225. 



(5) Jour, des Mines. Tome XXXIV., July, 1813. 



(6) liber die Bildung des Harzgebirges, 1842. 



(7) Massige Gesteine, 1st edition. 



