BY H. I. JENSEX. 10^ 



soiiite and fluorite; and amongst tlie rarer rocks we get pegmatites 

 carrying arfved.sonite, rutile, zircon, and fluor, panidiomorphic 

 trachyte with meliphanite(?), fluor, zircon, chalcedony, etc. 



4. Abundant tuffs, breccias and highly vescicular lavas are 

 represented (also at Mt. Flinders). 



5. Oligoclase is a commoner ingredient in the Fassifern 

 trachytes. 



The points specified show that the magma was rich in water, 

 fluorine, etc. 



The greater richness of the soil in the Fassifern district than 

 in other trachyte areas is readily seen to be due, in part at leasts 

 to the presence of oligoclase (carrying lime) in the trachytes, and 

 to the fact that segirine-augite (carrying MgO and CaO) largely 

 replaces true aggirine. 



The occurrence of alum in the Mt. Flinders breccia proves the 

 presence in it of sulphur-rich minerals such as nosean. Further, 

 the cobalt stains in the breccia and the amount of combined 

 nickel and cobalt oxides (0-07 %) in the lavas, show that here 

 again, on approaching the D'Aguilar Range, we enter a nickel- 

 iferous province, as I have indicated in my paper on the " Geology 

 of the East Moreton and Wide Bay." Such a high percentage 

 of NiO.CoO is not met with in the New South Wales trachytes. 



It might further be pointed out that in the Flinders- Fassifern 

 alkaline province — 



1. The same minerals are met with as in other Australian 

 alkaline provinces, though the lime-percentage is slightly greater. 



2. The same volcanic sequence occurs, and the same associated 

 rocks as in other alkaline provinces. The monchiquites of the 

 Nandewars and essexites of the Mittagong area are here repre- 

 sented by analcite-dolerite (teschenite), and this rock is older 

 than the trachyte. After this the sequence is from the more acid 

 to the more basic. 



3. The craters of eruption are situated mainly along two great 

 fissures which bound the senkungsfeld area of the Walloon Coal 

 Measures, in the same way as I have hinted that the Warrum- 

 bungles may be a senkungsfeld area, and I have shown that a 

 subsided area exists west of the Nandewars. 



