172 Alfred Sarker — Various Crystalline Rocks. 



planes, and often so massed together as to prevent their free develop- 

 ment. It constitutes nearly half the bulk of the rock. The colour 

 is an intense grass-green, the absorption being, parallel to a yellow- 

 green, ^ and 7 deep grass-green, almost opaque. The extinction- 

 angle c 7 is high, perhaps as much as 20°, but cannot be determined 

 precisely owing to the strong absorption. 



The other constituents are little crystals of finely lamellated 

 plagioclase, irregular grains of an untwinned felspar, apparently 

 orthoclase, shapeless granules of opaque iron ore, and a little clear 

 quartz occurring interstitially among the hornblende and other 

 minerals. 



(iv.) Quartz-Diorite from Viti Zevu, Fiji. 



This rock occurs in the cutting for a new road on the mountains 

 to the south of the Wainamala valley, below Narokorokoyawa in the 

 island of Viti Levu. It was collected by Mr. J. J. Lister during the 

 voyage of the " Egeria " in 1889. It is a crystalline rock showing 

 lustrous black crystals of hornblende, about a quarter of an inch 

 long, and flakes of golden-brown mica, in a mass consisting mainly 

 of felspar. The specific gravity is 2-778. 



Sections [1256, 1257] show that the felspar is exclusively plagio- 

 clase, in idiomorphic crystals, in which the usual albite-lamellation 

 is combined with Carlsbad and sometimes with pericline-twinning. 

 A strongly marked zonary structure is apparent in polarized light, 

 the extinction-angles being much wider in the interior than in 

 the border. There is clearly a transition in each crystal from a 

 thoroughly basic to an intermediate felspar. The hornblende, often 

 twinned, is of the green pleochroic variety found in the syenites 

 and most true diorites, aud the mica (biotite) is brown with intense 

 dichroism. These two minerals are often closely associated, and, for 

 the most part, mould the felspar. Quartz occurs interstitially as 

 the latest product of consolidation. The earliest-formed minerals 

 are apatite and magnetite, which are enclosed by all the other 

 constituents. 



The specimens are quite fresh, and, as regards the mutual relations 

 of the minerals, the zoning of the felspars, etc., agree well with 

 some examples of the Banatite type of quartz-diorite, such as those 

 from Hodrics near Schemnitz [1085] and from Ben Nevis [397], 

 or some of the Banat rocks themselves. Wichmann,' in his account 

 of the Fiji rocks, has described a diorite from near the same locality ; 

 but it is clearly of a different type, and he makes no mention of 

 either quartz or mica. 



(v.) Uralitized Gabhro from Eua, Tonga Islands. 



This specimen, also from Mr. Lister's collection, is from a boulder 

 on the east coast of Eua, but the position in which it occurs proves 

 that it must belong to the island itself. The point is one of some 

 interest, as Eua, like the rest of the group, ajjpears at first sight to 

 be built entirely of volcanic and calcareous rocks. The rock is a 



1 Tsch. Min. u. petr. Mitth. (n.s.) vol. v. p. 17 ; 1883. 



