Notices of Memoirs — Tertiary Alkali Rocks, Victoria. 471 



and may be Palaeozoic. Recent work (2), however, has shown, 

 especially in the case of the Omeo rocks, tliat they are probably of 

 mid- or even of late Tertiary age. The alkali rocks of Frenchman's 

 Hill, described by Howitt as intrusive orthophyres, consist really in 

 the main of lava-flows of anorthoclase trachyte which has a very 

 scoriaceous margin to the flows. There is a central plug of a coarser 

 quartz-bearing rock allied to solvsbergite and a more or less radial 

 system of dykes which are principally trachytic in character. Some, 

 however, contain quartz, one at least is a bostonite, and six or seven 

 prove to be dykes of nepheline phonolite. The district is one which 

 has been affected by a succession of elevatory movements of the 

 plateau type since the mid-Tertiary period, and, according to Griffith 

 Taylor (3), a more or less meridional Senkungsfeld runs through the 

 Omeo District a few miles east of Frenchman's Hill. The rocks of 

 Mount Leinster in Benambra consist principally of solvsbergites, 

 bostonites, and pyroclastic rocks of alkali trachyte. Petrologically 

 and chemically many of the rocks of Mount Leinster and of French- 

 man's Hill closely resemble some of the alkali rocks of Mount Macedon, 

 and, like them, are probably of mid-Tertiary age. The district has 

 been elevated at intervals during the Tertiary period, but physio- 

 graphically has not been closely studied. 



About 14 miles north-east from Mansfield in North-Central 

 Victoria and about 3 miles from Tolmie, in the Tolmie Highlands, 

 there occurs a volcanic hill, known locally as Gallows Hill, which 

 has recently been shown to consist of a volcanic centre of probably 

 late Tertiary age and to consist of lava-flows of nepheline phonolite. 

 From a locality near Barwite, east of Mansfield, another nepheline 

 phonolite has been found, but its field relations are at present uncertain 

 and no account of either of these rocks has yet been published. 

 Fenner (4) has recently shown that block elevation and depression 

 have affected the Mansfield area in recent geological times, and that 

 Gallows Hill lies near one of the fault scarps. 



The best-known area of alkali rocks in Victoria is the Mount 

 Macedon District, about 40 miles north-west of Melbourne (5). 

 The series is of mid Tertiary to late Tertiary age, and the rock 

 sequence from below upwards, while not always demonstrable, appears 

 to be as follows : anorthoclase trachyte, solvsbergite, anorthoclase 

 basalt, macedonite, woodendite, anorthoclase-olivine trachyte, olivine- 

 anorthoclase trachyte, limburgite. Immediately succeeding these 

 alkali rocks come lava-flows of normal basalt and of andesitic basalt. 

 The new types macedonite and woodendite contain over 1 per cent 

 of P2O5, and are related to the orthoclase basalts and to the 

 mugearites. 



While this part of Victoria shows evidence, by the existence of 

 more than one elevated peneplain, of successive movements of the 

 plateau type, no definite evidence of faulting or differential movement 

 has been recognized in the district. In the western district of 

 Victoria more or less extensive lava-flows of anorthoclase trachyte 

 occur near Coleraine, Carapook, etc. (6). Generally the trachytes 

 appear to be older than the newer basalts, but near Coleraine a dyke 

 of trachyte penetrates a small hill composed of a basic rock resembling 



