fissility. The constituents arc saussurite and dark aggregates of diallagc and 

 hornblende. These constituents are more or less lenticular in form, and the 

 flat surface of the lenticles lie parallel to each other, thus producing the 

 foliated structure. The gabbro-schist is a rock of finer grain, with a strongly 

 marked schistosity. It can be broken into flat slabs like a hornblende-schist, 

 to some varieties of which it bears the closest possible resemblance. Although 

 it is convenient to use the two terms flaser-gubbro and gabbro-schist, it must 

 not be supposed that there is any hard and fast line between the rocks 

 designated by these terms. They shade into each other by the most 

 insensible gradations. One very interesting structural variety, in 

 some respects intermediate between flaser-gabbro and gabbro-schist may be 

 termed augen-gabbro. In this variety the streaks which define the schistosity 

 sweep round " eyes " of diallage, which thus remind one strongly of the 

 "eyes " of felspar in augen-gneiss (see plate XXVI). Foliated gabbros arc 

 admirably shown at Karakclews Headland, and north of the small bay locally 

 known as Pen Voose, near Landewednack. The foliation is, doubtless, the 

 result of the regional metamorphism which has affected the district since the 

 formation of the gabbro. We have at present no very reliable evidence as to 

 the age of the gabbro, or of the regional metamorphism. The occurrence of 

 serpentine and gabbro at Nare Point, in association with Ordovician rocks, 

 has been already referred to (see ante, page 123.) If the former are intrusive 

 then they must be of post-Ordovician age. The Lizard gabbros are nowhere 

 seen in relation with fossiliferous sediments, but they are probably of the 

 same age as those of Nare Point. The apparent absence of pebbles of 

 serpentine and gabbro from the conglomerates north of Porthalla is negative 

 evidence which tells in favour of the view that the igneous rocks are of later 

 date than the adjacent sedimentaries. 



Next in importance to the Lizard gabbros are those of Anglesea and the 

 Lake District. The Angelica gabbros have been described by Professor 

 BONNEY. (1) Here, as at the Lizard and elsewhere, the} r were associated with 

 serpentine. They occur in the Avestern district, in Holy head island, and the 

 adjacent portion of the mainland. They consist of altered felspar and 

 diallage ; olivine is not mentioned as a constituent. In texture they may be 

 either massive or schistose, and Professor BOXXEY mentions that " on the 

 bank of an inlet near Tyddyn Gob is a rather schistose rock, which in the 

 lower part resembles a foliated gabbro, in the upper a schist." 



The Lake District gabbro occurs in the neighbourhood of Carrock Fell, 

 and is remarkable for its intimate association with an acid augitic granophyre, 

 into which it passes by insensible gradations, and also for the fact that it 

 contains quartz as an original constituent. It is the plutonic representative 

 of the andesitic dolerites. The rock was originally described by Mr. WARD (2) 

 as a hypersthenite, under the impression that the dominant pyroxenic 

 constituent was hypcrsthene. 



Dr. TRECHMANN has pointed out that the supposed hypersthene is in 



(1) Q.J.G.S. Vol. XXXVII., 1881, p. 40. 



(2) Q.J.G.S. Vol. XXXII., 1876, p. 16. 



