330 N. R. Junner: 



in character, and is frequently vesicular. Further down the slopes 

 of Garden Hill, the basalt is a dark compact fine grained type. Ao 

 stratigraphic determination of the age of the basalts is possible, 

 since they overlie leads whose age also is in doubt. The basalt at 

 Greensborough is older than the newer basalt to the east of Mel- 

 bourne, since a tongue of this basalt has filled up the old valley, 

 which has been cut near the junction of the older basalt and gravels 

 with the Silurian. On petiological and physiographical grounds 

 the writer has no hesitation in correlating it with the older 

 rather than the newer basalt. The 1902 geological map of Victoria 

 issued by the Geological Survey shows the Greens1)oi-ougli basalt as 

 older basalt and the Kangaroo Grounds type as newer basalt. 

 A later mai? published by the same department shows both as older 

 basalt. More certain evidence of their age is obtainable physio- 

 graphically. Jutsoni mentions that the Kangaroo Grounds basalt 

 is a monadnock in the peneplain. He2 also has shown that the 

 age of the peneplain is probal)ly kalimnan, tliat is, lower pliocene^ 

 or upi3er miocene. This being so, the age of the basalt is prepliocene 

 and probably miocene. The brief investigation of this point by the 

 writer supports the view that the Kangaroo Grounds basalt is a 

 monadnock, and that vei-y little vertical erosion occurred between 

 the filling up of the river valleys by the basalt, and the final pene- 

 planation. At Greensborough the evidence is less certain, but 

 petrologically these basalts appear to be identical, and the writer 

 believes therefore that thev Avere both extruded towards the end 

 of the peneplanation, and therefore their age is probably miocene. 

 The Garden Hill basalt occurring at the highest point of Kangaroo 

 Grounds is much more scoriaceous, and has a smaller specific 

 gravity than the main Kangaroo Grounds basalt, and is possilily 

 of more recent age. 



5. — Structural Features. 



(a) Foldiuff, crumpled aididines ; zones of crushing. 



The Silurian sediments have been normally and fairly openly 

 folded throughout most of the nrpa. The major axial lines in the 

 east of the area have l)ecn inajiped by .Tutson. The positions of 

 these have been verified by tlie author, and, in additi(ui, a few 

 minor folds have been located. A major fold is well seen in a 

 railway cutting near Greensborough station, and the same fold has 



1 b, p. r.02. 



2 1), p. 4yy. 



3 F. Chupiuaii. A stiul.v of tli l{.iti"»foi'<l liinistorK-. I'l-oc. l{oy Soc. Vict, vol. xxii. (ii.s.), I't. II. 



