THE VICTORIAN NATURALIST. 11 



movement of the latter took place at the second disturbance, 

 which might explain the rather high angle of inclination of some 

 of these beds. 



The Geological Survey of Victoria, in its recently published 

 Quarter Sheet * (the country surveyed in which approaches closely 

 to but does not include Mount Shadwell), divides the volcanic 

 rocks of the district into an older and a newer series. Whether 

 they coincide with the two sets of beds described above can only 

 be ascertained by further examination ; but the independent 

 determination by the Survey of two distinct periods of volcanic 

 activity in other parts of the same area is interesting, and some- 

 what confirmatory of the views expressed herein. 



In conclusion, I desire to offer my warm thanks to Mr. F. 

 Chapman, A.L.S., for his determination of and notes on the 

 specimens referred to in the Appendix, and also for his interest 

 and advice in connection with this paper. Mr. T. S. Hall, M.A., 

 has also been good enough to direct me to some of the scanty 

 references to Mount Shadwell. 



Appendix. 



Notes on Some Rocks and Minerals from Mount Shadwell. 

 By Frederick Chapman, A.L.S. 



S2}eci»ie7i i (from the " black beds"). — This is a portion of an 

 Olivine bomb. It has the usual granular character and apple- 

 green colour of fresh specimens. Here and there amongst the 

 granules are blebs of a darker mineral, which is proved by 

 microscopical examination to be Diopside. The cleavage is 

 very distinct. Its extinction angle with the crystallographic axis 

 c is rather less than that of typical Diopside. The pleochroism 

 is generally feeble, but sometimes shows a range from pale 

 yellow through yellow-brown to pale green. The optical sign is 

 positive. One of these crystals of Diopside includes numerous 

 parallel plates of a serpentinous mineral, which is a secondary 

 metasomatic change referable to Schiller structure. In the same 

 slide there occurs a granule of Bronzite showing strong cleavage 

 and marked refraction. The Olivine forming the mass of this 

 rock shows an incipient change by the separation of some of the 

 iron in the form of magnetite. The striking purity of these 

 Olivine nodules resembles that of the nodules found in the 

 Tertiary basalts of the Eifel, Germany. The conditions pertaining 

 to the occurrence of these nodules in Victoria would seem to 

 point to a segregation origin for these agglomerated minerals. 



Specwie'ii 2 (from the " red beds "). — A massive Olivine 

 rock, having a specific gravity of 3- 54- The specimen is mainly 

 composed of the ferriferous variety Fayalite, and it shows the 

 characteristic strong brachydiagonal cleavage of that mineral. 

 There has been a considerable amount of iron separated, in the 



* 8 N.E. (New Series). 



