[Proc. Koy. Soc. Victoria, 20 (N.S.), Pt. 1., 1907] 



A in' II. — Xofr on the De/position of Bedded Tuffs. 



By T. S. hall, M.A. 



Melbourne University. 



(With Plate II.). 

 [Read 11th April, 1907]. 



In many, it' mil most, of the places in South-western Victoria 

 where tuft's are displayed they are well stratified. These tuffs 

 a/re associated with the basaltic lavas which form such a featm-e 

 of the g-eolog}' of the State, and are referable to various parts 

 of the tertiary period. The volcanic rocks cover, according: to Sel- 

 wyn, somewhere about 9000 square miles, or about a tenth of the 

 total airea of Victoria. 



The tuffs with which we are at present concerned are usually 

 fawn-coloured, and vary with considerable irregularity in the 

 size of their constituent grains. They show a tendency to split 

 into flags along their bedding planes, and are fairly coherent, 

 8o that they are used, as in the neighboux'hood of Camperdown, 

 as a rough building stone. 



The decomposition of the tuft's and of the coarser scoria 

 yields a remarkably rich soil, and the porous subsoil affords both 

 natural drafinage and a capacity for storing up water. The tuffs 

 are then commonly tree-clad. 



Among the plaices which have come under my notice where 

 well bedded tuft's are to be seen are two belonging to the older 

 volcanic series, which is here seen to underlie the marine Bar- 

 wonian beds. One of these is at Curlewis, about eieht miles 

 east of Geelong, where on the beach platform a continuously dip- 

 ping series is seen extending for about four miles. The basalt 

 of similar age at Airey's Inlet is also associated with well bed- 

 ded tuffs which dip inland from the shore, pointing to the old 

 vent having been out at sea. 



Among the more recent tuffs which also show this character 

 may be enumerated those of Mount Leura and Bullenmerri, 

 near Camperdown. These beds cover a very large area. On the 



