part 4] NOEiTE OF siekea j.eone. 341 



Outer zone. — On the whole, the felspar shows slightly 

 increased turbidity, but inan}'^ cr3^stals are crossed by clear bands 

 containing gj-anules and microliths of hornblende and pyroxene. 

 The felspar-crystals are. moreover, separated by narrow clear areas 

 in Avhich granules of the ferromagnesian minerals occur. Much 

 additional micrographic felspar and augite is developed. 



Augite: inner zone. — This mineral is represented only by 

 plates and spongy masses of green hornblende, crowded with 

 innumerable regularlv-arranged microliths and clots of iron-ore; 

 even the iron-ore tends to disappear finally (see PI. XIX, fig. 5.) 



Outer zone. — The augite shows the usual additional precipi- 

 tation of iron-ore, and moreover is often traversed by brown 

 streaks developed along cracks and along certain twin-lamellae 

 [C 172 d']. These streaks are frequently accompanied by numerous 

 flakes of brown biotite ; the flakes, which are often parallel, may 

 extend outwards into the adjacent felspar [C 172 f/]. The augite is 

 generally fringed with green hornblende, which increases in amount 

 as the inner zone is approached. 



Hypersthene: inner zone. — Generally, only the inclusions 

 of iron-ore are recognizable ; the mineral itself has been converted 

 into green hornblende. 



Outer zone. — Often heavily charged with iron-ore, both in 

 the form of microliths and of a coarse graphic intergrowth with 

 the hypersthene. The mineral shows increasing alteration to green 

 hornblende. 



Olivine: inner zone . — The crystals are not recognizable in 

 this zone. 



Outer zone. — Much iron-ore is thrown down, with the develop- 

 ment of numerous brown and green serpentinous veins. The 

 mineral is sometimes converted into a mesh of vellow-s^reen 

 serpentine, with flakes of brown biotite around the margins 

 [C 172 f/]. Generally, however, it alters to green hornblende (see 

 PL XIX, fig. 6). 



(2) B. Alteration of norite by dolerite. — In one speci- 

 men [C 72] taken from near the contact, the felspars are turbid 

 and extensively altered, both to calcite and to a colourless mica in 

 the form of minute tufted flakes. The pj^oxenes are more or less 

 completely altered to green hornblende ; and much magnetite is 

 thrown down as a fine dust along innumerable cracks. 



In another specimen [C 172 5] hornblende is developed only 

 about the contact; elsewhere the ferromagnesian minerals are 

 largely altered to flakes of brov/n biotite. Much corrosion of the 

 older rock has taken place, and the junction with the dolerite is 

 very ill-defined. The felspar, for some distance from the contact, 

 shows evident recrystallization, and in its turbidity and minute 

 twin-lamellation it is scarce!}^ to be distinguished from the felspar 



