20 



J. B. Scricotor — Igneous Rocks of Singapore. 



suppose that the amphibole has been derived from rhombic pyroxene. 

 When the three minerals occur clustered together they are generally 

 accompanied by a considerable quantity of iron-ore. 



The rhombic pyroxene rarely shows good crystal outline, and then 

 only in the case of basal sections. The outline of the longitudinal 

 sections is generally rough, but the straight extinction can be 

 plainly seen parallel to the long axis of the sections and the cleavage. 

 In thin section the mineral is colourless or almost so. In sections 

 slightly thicker than the usual rock slide, however, and in grains from 

 the crushed rock, it appears coloured and gives a pale-green and pale- 

 orange pleochroism. The colour is faint, and the mineral must be 

 considered as being much nearer enstatite than hypersthene. 



Fig. 2.— Dyke-like mass of enstatite-vogesite in the hornbleude-granite of Pulau 

 Ubin, Singapore. (From a photograph.) 



Another specimen {b) was finer in grain than the last, and contains 

 the same minerals. The amount of quartz present is small. 



In the same quarry a big vein of a still finer-grained, dark reddish 

 brown rock (c) was seen standing out from the working face, where 

 the granite was being worked away on either side of it like a dyke, 

 and the same rock occurred close by mingled with the granite in sucli 



