METAMORPHIC ROCKS OF THE OMEO DISTRICT, GIPPSLAND. 207 



of moi'e recent practical research has led to some little under- 

 standing of the causes which have produced these effects which 

 one speaks of as metamorphic. 



In this paper I propose to record as a small contribution to 

 the study of the Crystaline Schists, the observations which I 

 have made upon the so called Regional Scliists of Omeo. Some 

 of the details have been already published, whilst the remainder 

 is now given in anticipation of papers at present in preparation. 



It will be well, once for all, and for the sake of clearness, to 

 dehne the sense in which I use the terms contact-, pressure-, and 

 regional-metamorphism, and I regard dynamo-metamorphism and 

 pressure-metamorphism as synonimous. 



By contact-metamorphism I understand these changes pro- 

 duced in rock formations by increased temperature, by mineral 

 solutions, by gaseous emanations, and probably also by increased 

 pressui'e all due to the proximity of invasive igneous rocks. 



By pressure-metamorphism I understand the eifects produced 

 upon rock masses, both sedimentary and igneous, by the direct 

 pressure of great earth stresses. These effects will therefore 

 include slaty-cleavage, the crushing of I'ock masses in situ, and 

 the stretching of rocks laterally and vertically. 



Regional-metamorphism as seen in the Omeo district seems to 

 be the resultant of both forms of metamorphism. 



GENERAL GEOLOGICAL FEATURES OF THE DISTRICT. 



It will be only necessary to say so much of the geological and 

 physical structure of the Omeo district as may suffice to bring 

 before the reader the general features of the localities to which 

 these notes refer. 



The Great Dividing Range in Eastern Victoria reaches to 

 almost its greatest altitude near Omeo. It thence rises in a series 

 of plateaux, which during a great part of the Tertiary period, if 

 not even in Mesozoic times, formed part of a great continuous 

 upland, which through subsequent erosion of river valleys, only 

 now shews its traces in isolated tracts of considerable elevation, 

 such as the Snowy Plains and the Dargo High Plains. The Omeo 

 plateau ascends by several steps, if I may so phrase it, rising 

 finally to the great and spreading downs of the Bogong. The 

 elevation of these plateaux lies between 2,500 and 5,500 feet 

 above sea level. Isolated mountains rise above them to the 

 maximum height of G,50U in Mount Bogoug. 



The geological structure of this part of the Australian Alps is 

 simple. A mountain mass is composed of sedimentary, plutonic 

 and volcanic rocks, wholly of Palaeozoic age, excepting where in 

 limited areas the older formations are here and there capped by 

 flows of basalt, which cannot well be older than the Middle 

 Tertiary.* 



* Geological Survey of Victoria .Progress Report IV, p. 110 ; R. A. F. Murray, Geology 

 and Physical Geography of Victoria, 1887, p. 111. 



