Lhnhurglte Rock. 131 



lavas are held to be of any age later than triassic. The 

 limburgite of the Macedon district is regarded by Professor 

 Skeats as of the last phase of effusion before the flow of the 

 newer basalt. 



The rock described by Mr. G. W. Card' from The Peak, Upper 

 Burragorang, bears a marked resemblance to the Balwyn rock 

 both in hand specimens and under the microscope, but differs 

 essentially in having a fair amount of nepheline disseminated 

 through the magma. A point in common between the two 

 rocks is the occurrence of inclusions of an exogenic character, 

 consisting of pyroxene and picotite in mutual association. 



One other rock occurrence of the limburp:ite type from Vic- 

 toria may here be mentioned, which is found in the form of 

 dykes cutting through the older rocks, and not as volcanic plugs 

 or necks. This is the series of basic dykes described by Mr. (after- 

 wards Dr.) A. W. Ho'witt as traversing the sedimentary rocks 

 in which the saddle reefs of Bendigo have been found.- Accord- 

 ing to Dr. Howitt these rocks have been injected into fissures 

 after the formation of the quartz reefs. This particular rock is 

 referred by Howitt to the limburgites ; and he remarks that 

 *■ The extraordinary freshness of some samples of this rock from 

 Bendigo suggests that it is of comparatively late geological age." 

 It may, therefore, belong to the same series of effusions as the 

 Woodend and Balwyn types. The mineralogical composition 

 of the above rock generally resembles both of the other types 

 just mentioned, as the following notes from Dr. Howitt's descrip- 

 tion show, although it differs from both those types in having 

 numerous crystals of amphibole in the ground-mass, whilst the 

 felspars are entirely absent : magma of very basic character ; 

 ground-mass with pale brown to colourless glass. Microliths and 

 skeleton crystals of amphibolite, often arranged in a stellate 

 manner around the magnetite crystals. Felspar absent. The 

 augite crystals follow the generation of microliths. Porphyritic 

 crystals of augite and olivine ; the latter colourless, ranging 

 from fresh to completely altered. 



1 Card, G. W. — "On the occuiTence of Nepheline in Post-triassic Basalts of the 

 Hawkesbury Sandstone Area." Ibid, vol. vii., pt. iii. (1903), p. 236. 



2 Howitt, A. W.—" Notes on Samples of Rocks collected in the 180 Mine at Bendi.yo.' 

 Special Rep. Dept. Mines, Victoria, 1893, pp. 3, 4. Mr. R. H. Walcott, F.G.S., of tlie 

 National Museum has kindly directed our attention to the above paper. 



10a 



