The Gneisses and Altered Dacites of the Dandenong District (Victoria), and their Relations to the Dacites and to the Granodiorites of the Area

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Abstract
I. I ntroduction . T he rocks with which this paper deals occur about 25 miles distant from Melbourne, in a direction a little south of east. The area is all included within the parish of Narree Worran, in the counties of Evelyn and Mornington. The oldest rocks in the district are sediments of Lower Palæozoic age, either Silurian or Ordovician; but with these the paper is not directly concerned. Intruded into these sediments is a mass of granodiorite, which is now exposed at the surface in the southern part of the area. To the north of the granodiorite lies an extensive area of hypersthene-biotite-dacite and quartz-porphyrite, which forms the Dandenong Hills. This rock series is also younger than the Older Palæozoic sediments, for in some places it appears to rest upon them, and in others to be intrusive into them. The boundary between the granodiorite and the dacite runs in an easterly direction, and while examining this junction in 1905 I discovered a belt of gneissic and altered rocks which for several miles come between the normal development of the granodiorite and of the dacite. It is with these rocks and their relations to the plutonic and volcanic series adjoining them that this paper deals. Hitherto gneissic rocks have been recognized in Victoria only in certain parts of the Western District and in North-Eastern Gippsland. These, however, are probably of Archæan age, and certainly have nothing in common with the foliated rocks described below. II. P revious L iterature . The origin, age, and field-relations

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