PRBSIDENt'.S address SECTION c. 203^ 



MIDDLE KAINOZOIC (?) 



Alkaj.i Series op Cextral and Western Victoria. 

 Geographical development. (See Map, Plate 4.) 



Central Victoria.- — In Ceutral Victoria alkaline rocks are fairly- 

 widespread in the Mount Macedon district. SoH'sbergite plugs occur 

 at Camel's Hump, the Hanging Rock, and Brock's Monument, Lava 

 flows of anorthoclase-trachyte and various more basic rocks gradually 

 merging into the newer iDasalts occupy many square miles to the 

 north of the divide at Mount Macedon, extending up towards the 

 southern flanks of the Cobaw Ranges, between Carlsruhe on W. and 

 Lancefield on E. At Upper Macedon and the Barringo Creek the flows 

 are south of the divide. 



Physiography. — The solvsbergite plugs form projecting masses : 

 Camel's Hump, 3,300 ft., rising about 300 ft. above the surrounding 

 dacite of Mount Macedon; Hanging Rock, 2,360 ft., rising 350 ft. 

 above the anorthoclase-trachj^e flows at its base; and Brock's Monu- 

 ment rising above the Ordovician sediments. Some of the trachyte 

 lava flows issued from parts near tlie summit of Mount Macedon, two 

 flows have a southerly trend — one down the valley of Barringo Creek, 

 and another bettei- deflned one, on whicli U. Macedon is built, forming 

 now a ridge between Turritable and Willimigongong Creeks. Other 

 flows started on the northern slojie of Mount ^lacedon, one from near 

 Braemar House, another from above Hesket, while others appear to 

 have originated from vents like the Jim Jim and Macalister's Rock, or 

 fissiires on the plains to the north. 



Geological Relations. — Prof. Gregory describes the alkali series 

 of rocks as starting with geburite-dacite, followed by solvsbergites, 

 trachyjjhonolites, and soda-andesites (176). He I'egards the dacite as 

 resting on a denuded siu'face of granodiorite. Mr. Summers and the 

 author, as the result of more extended work, the detailed results of 

 which will shortly be published, have come to different conclusions 

 concerning sevei-al of the geological and petrological problems in the 

 Macedon district. We regard the granodiorite and the dacite as con- 

 sanguineous, the dacite being the earlier extrusion from the magma, 

 and partly eruptive, partly effusive, while the granodiorite represents 

 a rather later more deep-seated intrusion. Analyses show that the 

 two rocks have almost identical chemical composition (see p. 193), 

 and contain only about 5 per cent, of alkalies. The Alkali series 

 is a much younger one of probably Mid-Kainozoic age, since the 

 later rocks merge into the newer basalts. Numerous analyses made 

 by Messrs. Bailey, Lewis, and Hall, of the Mines Departmeat (266), 

 support the field and microscopic evidence. The sequence of the rocks 

 fiom older to newer appears to be as follows: — Solvsbergite, anortho- 

 clase-trachyte, olivine-anorthoclase-basalt, anorthoclase; olivine- 

 trachyte, macedonite, olivine-anorthoclase-andesite, limburgite, newer 

 basalt. 



Western District. 



Geographical Distribution.— A\k&\i rocks occur at Coleraine, a 

 few miles to the North of Coleraine, at Carapook, Phoines, and near 

 Casterton (172, 17.3, 174, 175). 



