

PRE-CAPE ROCKS OF SOUTH AND WEST OF COLONY 45 



form, and brilliance of the stalactites attached to them. 

 Other caves, the entrance to which is often on the face 

 of cliffs along the sides of the valleys, await exploration 

 in the Cango district. The band of limestone in which 

 the great cave is situated is about 1,800 feet thick, but 

 when traced to the east or west it gradually becomes 

 thinner. The limestone in the Cango beds is crystalline 

 and dark grey in colour and usually contains some 

 magnesium carbonate, but in some localities it is suffi- 

 ciently pure to yield good lime. Occasionally oolitic 

 beds are met with, and when examined under the 

 microscope these are found to contain organic remains, 

 although no determinable shell has been seen. These 

 are the only traces of fossils hitherto found in the Cango 

 series. 



Slates and fine quartzitic grits form a great part of 

 the series. The slates are irregularly cleaved, and no 

 rock of use for roofing has been found amongst them. 



The intrusive rocks in the Cango district are nearly 

 all altered to such an extent that the original minerals 

 composing them have been replaced by others. At 

 present the chief components are the fibrous variety of 

 hornblende called uralite, green hornblende, augite, 

 epidote, chlorite, felspar, quartz, calcite, sericite, magne- 

 tite, apatite, and brown mica. The greater number of 

 the dykes were originally dolerites without olivine, made 

 up principally of augite and felspar ; some contained 

 much hornblende which still remains in the rock. The 

 augite has been mostly altered to uralite, but kernels 

 of the former mineral are still left within the patches of 

 fibrous hornblende. The rock has often an ophitic 



