196 Charles Fenner: 



The b<)\indaries between these five divisions are not artificial, but 

 natural. According to the belief of the writer, such boundaries^ 

 are in all cases dominant fault lines. Detailed discussion of these 

 important faults will be found in a later portion of the paper. 



VII. — The Rocks of the Area, 



Before entering upon the detailed account of hill and valley, we 

 may with advantage discuss the nature of the various types of rock 

 that occur, in so far as their nature and structure bear on the- 

 problems of physiography. For convenience we shall deal with the- 

 rocks in order of age : — 



(a) Strongly folded sandstones, quartzites, and slates (Lower 

 Ordovician). 



(b) Granites and Granodiorites. (? Silurian and ? Devonian.) 



(c) Glacial conglomerates and Sandstones. (Permo-carbo- 

 niferous.) 



(d) Older Basaltic lava flows. (Early to Middle Tertiary.) 

 ( e) Gravels, sands and clays. (Middle Tertiary.) 



(f) Newer Basaltic lava flows. (Later Tertiary.) 



(g) Gravels, sajids, soils, etc. (Post-Newer basaltic to Recent.) 

 (h) Dykes of various ages. ' 



The following notes should be read in conjunction with the* 

 geological map of Victoria : — 



(a) Lower Ordovician. — These rocks form, as far as is known, 

 the bedrock of the whole area; they also outcrop over a very large- 

 part, forming practically the whole surface of Block A, ,^<^st of 

 C, and part of D. They consist of sandstones, quar.tzites, grits, 

 and slates, intensely folded into anticlines and sypclines; these- 

 strike almost due north, with variations of a few degr^s east or 

 west. They have been enormously eroded, since in the past they 

 may have formed a land surface exposed to atmospheric erosion 

 ever since the close of the far-away Lower Ordovician period. 



In this connection, however, there are other possibilities that 

 must not be overlooked. For instance, A. R. C. Selwyn, in his: 

 Notes on the Physical Geography, etc., of Victoria, 1866 (ref. 50, 

 pp. 9, 10), draws att3ntion to the possibility that the upper palaeo- 

 zoic sediments of the Grampians area in the west, and the Mansfield- 

 Mt. Wellington area in the east may once have extended in a 

 ** broken and undulating anticlinal arch," right across the inter- 

 vening area. The accompanying diagram is but slightly altered 

 from that published by Selwyn, and suggests the possibility referred* 



