﻿246 DR. A. HOLMES ON THE TERTIARY [vol. lxxii, 



frequent association of camptonite and bostonite is in the Sanhuti- 

 River district paralleled by the association of picrite-basalt and 

 solvsbergite. The rock is also very similar to the limbnrgites of 

 the Macedon District, Victoria 1 (Tertiary alkali series), which, like 

 the Mozambique picrite-basalt, are associated with anorthoclase- 

 bearing rocks. The main outstanding feature of the analysis is 

 the high percentage (for this class of rock) of ferric oxide. This 

 is due to the preponderance in the rock of augite, and to the 

 abundance of magnetite. Titaniferous augites frequently show an 

 excess of ferric over ferrous iron ; the Bail-Hill example is a case 

 in point. 



Rocks of Group B. 



XIV. Basalts: Sills and Dykes. 

 (PI. XX, fig. 6 & PI. XXI, fig. 1.) 



The specimens collected 3 are slightly vesicular rocks from the 

 following localities : — 



128, 129, 130. Sill, west side of Sokoto Hill, at the base. \ Dark re 

 142. Dyke, near Ibrahimo. J ar ^ re ^' 



141. Dyke, Mochelia (reddish brown). 



These rocks are of even grain and fine texture, and consist 

 essentially of a . mesh of lath - shaped felspars, between which 

 groups of granular augites are contained. Olivine has in all cases 

 been altered to serpentine, and the latter is only a minor constituent. 

 Filling up the interstices of the crystalline network is a grey- 

 brown glass swarming with dark globulites, or with branching 

 sprays of magnetite. Examined closely, specimens from Sokoto 

 Hill and Ibrahimo are seen to be pitted with minute green-lined 

 vesicles or amygdales. The first stage in the infilling of the latter 

 is represented by a fibrous green mineral. The same mineral occurs 

 in greater quantity in the amygdaloids ; and, since it contains 

 alumina and has a refractive index greater than 1*576, it may be 

 referred to one of the chlo rites. The main body of the amyg- 

 dale occasionally consists of brown or greenish-brown palagonite; 

 but more usually it is occupied by chalcedony, with which 

 opal is sometimes associated. The minute amygdales of the 

 Mochelia dyke appear to be free from a chloritic lining. • 



The felspar occurs chiefly in small tabular crystals accompanied 

 by a sprinkling of larger individuals, indicating an approach 

 to porphyritic texture. This appearance is intensified by the 

 bunching together of some of the smaller crystals in parallel or 

 divergent series. Extinction-angles, twinning, and refractive index 

 (1*560) show that the species is labradorite. Many of the 

 larger crystals enclose patches and shreds of chlorite, and lines 

 of globulitic glass-inclusions immediately within their outer borders 



1 H. S. Summers, Proc. Roy. Soc. Vict, n, s vol. xxvi (1914) p. 278. 



2 A number of dark compact dyke-rocks collected by Mr. Wray (from the 

 district of Pernao Vellosa Harbour and from Makulia farther north) were 

 lost during transit to England. 



