The Lake Fault Oil-Gold 



from igneous rocks such as gabbro, or some other basic 

 rock. 



The changes which are brought about by the action 

 of pressure and shearing are partly physical, resulting in 

 the development of new structures, such as the banding 

 or " foliation " described above, and partly chemical, 

 resulting in the production of new minerals. The 

 changes are summed up under the term metamorphism, 

 and the materials which have undergone such changes 

 are spoken of as metamorphic rocks. 



From their general appearance and their position 

 with regard to the Older Palaeozoic rocks above the 

 thrust-plane, we concluded that these rocks belonged to 

 the Archaean group, the oldest known rocks. 



There were in addition to the coarse-grained gneisses 

 certain finer-grained rocks in the complex. These pos- 

 sessed a structure somewhat similar to that of the gneisses, 

 but the folia were thinner. They are called schists, and 

 were of several different kinds. One kind in which 

 mica and quartz are the principal constituents is called 

 mica schist, and has in all probability been formed by 

 the metamorphism of ancient sediments, such as mica- 

 ceous sandstones or grits. 



Another kind occurred in long narrow bands travers- 

 ing the granitoid gneisses from north-west to south- 

 east, and consisted of a dark olive-green mineral, 

 chlorite. 



These are chlorite schists, and may have been formed 

 from dykes of basalt or of dolerite, which were intruded 

 into the great igneous complex before the metamorphic 

 forces came into play. 



There were also to be seen dykes of dolerite and 



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