[I'Roc. K'oY. S<H. Victoria 27 (N.8.), Pt. II.. 19U]. 



Art. XVIII. — TJte Petrology of the Igneous HocLs near 

 HeaUsville and Narhetli()t)g. 



By NORMAN R. JUNNER,' B.Sc. 

 (Caroline Kay Scholar in Geology, University of Melbourne, 1913). 



5. i'ield Relations and Origin of the Eocks : — 



(a) Eelationship of the Granodiorite to the Sedi- 



mentary and Volcanic Rocks. 



(b) Relationship of the Volcanic Rocks to one 



another. 



(c) Origin of the Rocks. 



6. Conclusions. 



1. — Introduction and Physiography. 



The area described in this paper consists chiefly of an elevated 

 series of ancient volcanic rocks, probably Devonian in age. The 

 relief is marked, Mount Donna Buang and other peaks rising to 

 more than 4000 feet above sea-level, Avhilst the bed of the Yarra at 

 Healesville is less than 300 feet above the same datum. The Silurian 

 sediments on the north side of the Victorian Main Divide which 

 passes through this area, have an average elevation of between 1000 

 and 1200 feet, but they rise to more than' 2000 feet above sea level 

 in places. Within the area described the divide is entirely in 

 volcanic rocks. The northern streams, of which the most important 

 is the Acheron river, flow into the Goulburn river, whilst the 

 Bouthern streams all drain into the Yarra river. Waterfalls are 

 present near the heads of most of the streams. They are principally 

 determined by joint planes in the volcanic rocks, e.g., Stevenson's 

 falls and the Acheron falls. The Mever's creek falls, however, are 



