Geology of Wurro n<l]jt(' Goldjield. 551 



Summary. 



The paper deals with the siluriau rocks of a wide area of 

 country in the basin of the Yarra. 



The rocks are shown to consist chiefly of shales and sand- 

 stones, with a series of fossiliferous grits and conglomerates at 

 Warrandyte. 



The geological structure of the silurian consists principally 

 of a great arch or geanticline at Warrandyte, on the top of 

 which are a series of minor folds, with which are associated the 

 conglomerates and grits, and a series of auriferous quartz reefs. 

 Tiiis fold is known as the Warrandyte Anticline. It extends 

 from Tunstall to Watson's Creek, and its axial line is broken at 

 Warrandyte. To the south and north of Warrandyte it breaks? 

 into more nornuil folds, which are described. To the west of 

 the Warrandyte Anticline is the BuUeen Syncline, a great 

 feature traced some distance north and south. Farther west is 

 the Templestowe Anticline. Various dykes are associated with 

 the rocks. 



Tbe evidence of faults and peculiarities of joints in the 

 silurian is discussed, including the smooth fracture of con- 

 glomerate pebbles. 



The conditions of sedimentation in the silurian are referred to. 



The age of the silurian rocks cannot be settled until the 

 fossils are examined. On field evidence alone, the oldest beds 

 are at Warrandyte, and the youngest at the BuUeen Syncline, and 

 to the north of Croydon. 



The thickness of the western leg of the Wan-andyte Anti- 

 cline is estimated at between 12,000 and 13,000 feet, and that 

 of the eastern at between 14,000 and 15,000 feet, while the 

 vertical height of the silurian removed from above the War- 

 randyte Anticline is probably over 12,000 feer. 



The rocks from which the silurian conglomerates were de- 

 rived are shown to be altered and unaltered sedimentary rocks. 



The Warrandyte goldfield is shown to be due to a series of 

 minor folds on the top of the Warrandyte Anticline, which have 

 fractured and so admitted the silica and gold. The distribution 

 of the quartz reefs is noted, and their relation to the folds and 

 the dykes to the east is discussed. The conchision is drawn 



