Art. III. — The Diorites and Granites of Swift's Creek, 



and their Contact Zones, with Notes on the 



Auriferous Deposits. 



By A. W. Howitt, F.G.S. 



[Read 12th June, 1879.] 



Introduction, and Description of the Physical 

 Features of the District. 



It is now nearly fifteen years since my attention was first 

 directed to the peculiar physical and geological features of 

 the Swift's Creek District, near Omeo. During that long 

 period I have from time to time made observations as to 

 the rock masses found there, but it was not until five years 

 back that I seriously set myself to the task of systemati- 

 cally collecting data, and of endeavouring to trace out and 

 explain therefrom their geological history, while describing 

 and classifying the various formations occurring at that 

 place. Before recording the results of these observations on 

 the geology of Swift's Creek, it may be as well to describe 

 shortly the physical geography of the part of Victoria in 

 which that place is situated. 



If we take a general view of Eastern Victoria, we shall 

 perceive that it consists of a vast extent of mountains, 

 known as the Australian Alps, which are flanked to the 

 south by lower lying tracts, stretching from the foothills to 

 the sea, and to the north by the extensive levels of the 

 Murray basin. The central mountain mass may be further 

 described as being formed mainly of highly-inclined Lower 

 paloeozoic strata, on the denuded edges of which rest isolated 

 tracts, either of upper paloeozoic formations, or of Tertiary 

 volcanic streets. 



The mountainous area rises to heights of nearly 7000 feet 

 above the sea level, and snow accumulates upon them for 

 many months of the year. The formations of Tertiary age 

 which fringe the mountains on each side rise on their flanks 

 to elevations which do not, according to my measurements, 

 exceed 800 feet above sea-level, and often fall short of that 

 height. If we, therefore, picture to ourselves a contour line 

 extending from the south-eastern boundary line of this 



