268 



PETROLOGICAL NOTES, 11. 



The Pegmatites occur in two series of veins and dykes, one set 

 ■closely associated with microgranite, the other cutting it. The 

 older can be seen occurring as irregular blebs, in a microgranite- 

 dyke near the deepwater-jetty, where it also forms a border to 

 the dyke at intervals. The younger occurs intersecting micro- 

 granite in the railway-cutting south of the town-jetty. Both 

 sets are exposed on the shore, north of the deepwater-jetty, where 

 a N.W.-S.E. series cuts and faults a N.E.-S.W. set. 



Aplite occurs only rarely, and its age is doubtful. It is older 

 than the pegmatites, as the old one cuts it at the deepwater- 

 jetty, but its relation to the microgranite has not been observed. 

 It has intruded the gneiss, both transgressively and concordantly, 

 on the coast, where the contorted zone appears, between Mts. 

 Clarence and Adelaide. 



Darwin recorded two series of basic dykes on the south side of 

 the harbour. They cannot be distinguished on the north, as 

 only a few dykes and veins occur. One dyke, near the deep- 

 water-jetty, can be traced some distance seawards; it cuts gneiss, 

 microgranite, and pegmatite, and is crammed with corroded 

 xenoliths of acid rocks and xenocrysts of felspar. The smaller 

 fragments are often associated with patches of sulphides. Some 

 basic veins are to be seen in the railway-cutting, and on the 

 shore, near the baths. They are marginally chilled, and cut 

 microgranite and pegmatite. A slide of the junction of one of 

 these veins with the gneiss, shows the cataclastic structure of 

 the gneiss very well, while the basic rock is exactly like the 

 so-callt^d andesites of the goldfields. 



The microgranite, aplite, and pegmatites seem to be related, 

 but there is nothing to show whether they are directly connected 

 with the granodiorite or not. 



There are numerous examples of miniature faulting in the 

 district. 



For Roelands District, see N0.II6A of 40 chain Maps, Lands 

 Survey Department, West Australia. 



