part 4] JS-QRITE OF SIEREA LEONE. 345 



Fig-. 4. Enstatite-dolerite [C 163], south of York. The section con- 

 sists principally of zoned plagioclase and angite. In the top left- 

 hand quadrant is a patch of clear untwinned felspar, enclosing 

 grains of pyroxene and numerous small needles of apatite ; also it 

 partly encloses an irregular plate of augite. Interstitial to the 

 laths and prisms of plagioclase, and also enclosed in the areas of 

 clear felspar, is much granular pyroxene, in the form of both com- 

 mon augite and enstatite. The felspar-prisms each consist of 

 turbid labradorite surrounded by a narrow zone of clear felspar. 

 In the lower half of the figure is a sj)ongy mass of iron-ore. 

 Ordinary light. X 28. (See p. 324.) 



5. Primary intergrowth(binary) of felspar and augite [C68], 



Lumley. The figure shows fine and coarse grains of augite 

 embedded in clear labradorite. The bigger grains, arranged in rude 

 graphic fashion, are in optical continuity with the augite that 

 encloses the large plates of magnetite. Ordinary light. X 28. 

 (See p. 331.) 



6. Primary intergrowth (ternary) of felspar, augite, and 



magnetite [C68], Lumley. The minerals depicted are felspar 

 (white), augite (dark grey), and magnetite (black). The magnetite 

 is largely enclosed in augite that shows characteristic cleavage. 

 Parallel tongues of augite, each enclosing a rod of magnetite, 

 project into the felsi^ar. Near the intersection of the cross-wires, 

 in the upper right-hand quadrant, the ternary intergrowth is beauti- 

 fully developed in the form of fine parallel rods of the three com- 

 ponent minerals. In several parts of the slide the augite is seen to 

 be graphically intergrown with the felspar. Ordinary light. X 28. 

 (See p. 333.) 



Plate XIX. 



Fig. 1. Corona-like intergrowth of felspar and augite [C68], 

 Lumley. The intergrowth was formed later than that shown in 

 PL XVIII, fig. 5. The minerals depicted are labradorite (i^ale grey), 

 the intergrowth (dark grey), and magnetite (black). The clear 

 spaces represent fragments of the slide that have broken away. 

 The intergrowth is seen spreading fan- wise into the felspar from 

 the contact of this mineral with the magnetite. The felspar- 

 crystal enclosed in the magnetite has been largely replaced by the 

 intergrowth. Ordinary light. X 28. (See p. 331.) 



2. Graphic intergrowth of hypersthene and magnetite, 



normal norite [C 1], Leicester Peak. The minerals depicted 

 are the following: — felspar (white), with faint cleavage-cracks; 

 olivine (pale grey), with thick irregular cracks ; hypersthene 

 (medium grey), with a fine parallel cleavage ; augite (dark grey), 

 locally almost opaque with schiller inclusions; and magnetite 

 (black) . In the central portion of the section, with a large crystal 

 of olivine on the left and a smaller crystal of augite on the right, 

 is an irregular plate of hypersthene in which abundant graphic 

 magnetite is embedded. The magnetite appears also as large plates 

 in the hypersthene. Ordinary light. X 28. (See p. 332.) 



Figs. 3 & 4 illustrate the alteration of norite by a magma of similar 

 composition ; namely, beerbachite. 



3. Corroded xenolith of olivine and hypersthene in beer- 



bachite [Mount Aureol, No. 3]. The left-hand half of the 

 section consists mainly of olivine, and the right-hand half mainly 

 of hypersthene. These minerals have been so extensively corroded 

 that they now form merely a spongy network with interstices 



