IFIE DOLERITES OF KING OBOKUK I,\NI> \ND ADKME LAND- BROWN K. 257 



an interstitial role. This pyroxene is entirely iiuiiuicliiuc. and has a violet, or rather 

 rose, colour, with distinct pleochroisiu. betokening the presence of titanium. Biotite 

 i> ulinndant. likewise ilmenite in semi-skeletal forms and rods. Apatite is scarce, and 

 t here are a few irregular patches of pyrites. 



The rock is considerably altered, the felspar being spangled with sericite flakes 

 as well as with calcite and chlorite ; in some places it appears to be altering to a zeolite. 



Augite is much changed to a fibrous uralite, pleochroic as follows : 

 X = Pale yellowish-green. 

 Y = Green. 

 Z = Bluish -green. 



With Y>Z>X. 



With the uralite change, there has been separation of iron oxide. Chlorite is 

 another alteration product of the pyroxene. Biotite is irregularly bleached. Some 

 of this mineral is probably primary, but much appears to be an alteration product of 

 the augite. The section of an augite crystal is often covered over with tiny scraps of 

 biotite, many of which are optically continuous and simulate the appearance of a graphic 

 intergrowth with the augite. Some of the biotite and uralite contain pleochroic haloes 

 surrounding tiny indeterminate colourless minerals. A number of irregular patches 

 of yellow-green chlorite are seen, sometimes associated with little granules of carbonates 

 and of secondary sphene ; these may represent the ultimate alteration products of 

 augite. 



The rock may be termed an essexitic dolerite. (Plate XXXIX, Fig. 6.) 



