394 PROCEEDINGS OF SECTION C. 



THE METAMORPHIG ROCKS OF STATION PEAK. 



These have a very limited distribution at the surface, being confined 

 to a small crescent-shaped area about 200yds. wide, from east to west, 

 and half a mile long from north to south, flanking the extreme south- 

 west exposure of the granite of the You Yangs. Their extent is indi- 

 cated on quarter-sheet 19, S E of the Geological Survey of Victoria. 



No doubt both granite and metamorphic rocks extend beneath the 

 sheet of basalt which surrounds the You Yangs. The Metamorphic 

 rocks which are exposed at the surface have been much denuded, and 

 now form merely a thin coat overlying the granite. They consist of 

 highly altered sediments, marked on the map as probably Silurian, while 

 the legend on the map refers them to Lower Silurian — that is, Ordo- 

 vician, as now understood. Their age cannot be fixed with certainty,, 

 but, since they lie 30 miles west of Melbourne and Ordovician rocka 

 occur to the north and north-west along their line of strike, it is probable 

 that these rocks are highly altered Ordovician sandstones and mud- 

 stones. For the most part they can be studied only from surface 

 fragments lying in a plantation. The best exposure is seen in a ditck 

 running east and west at the south end of the plantation, at the nortk 

 extremity of the road from Lara, shown on quarter-sheet 19 S.E. 

 In this shallow section the junction with the granite can be seen, and 

 the strike of the metamorphosed sediments is here a little to the west 

 of north, which agrees with the general strike of the Ordovician rock& 

 in Victoria. It is almost impossible to get specimens of the rocks whicL 

 are unweathered, but some fairly fresh pieces were obtained and sec- 

 tioned. Along the line of contact fragments of tourmaline and tour- 

 maline-bearing rocks were found, and an examination of rock sections 

 of the altered rocks shows that the extreme metamorphism near the 

 contact with the granite has been brought about not only as a result 

 of thermal metamorphism, but, in addition, by the passage of hot gases 

 and solutions containing boric acid, &c., through the sediments near the 

 junction of the granite. The result has been, as an examination of the 

 section shows, that the sandstones and mudstones have been meta- 

 somatically altered and completely recrystallised. All signs of clastic 

 structure in the minerals and all traces of bedding are lost in the rock 

 in contact with the granite, but one of the less altered rocks away from 

 the contact shows traces of the original bedding, where layers of sand 

 and clay have been converted into secondary quartz and micas. 



DESCRIPTION OF THE METAMORPHIC ROCKS— LEAST ALTERED 

 ROCK AWAY FROM THE GRANITE CONTACT, SECTION 392. 



Megascopic Examination. — This rock was probably an argillaceous 

 sandstone, with alternating laminae of quartz and clay. It now has a 

 spotted appearance, as the result of metamorphism, but the original 

 bedding planes can still be traced. 



Microscopic Examination. — Traces of the original bedding can be 

 seen in the linear arrangement of quartz and micas. The quartz has been 

 entirely recrystallised, and now consists of interlocking crystals. The 

 mica is of two kinds. The most abundant is a clear white mica. Although 



