June, 1907.] THE VICTORIAN NATURALIST. 21 



fore, directed to sections along the creek, some little distance 

 above the rifle-butts. Here quite enough was found to occupy 

 the attention of the members for the short afternoon. Various 

 characteristic structures in the basalt were noted. The mouth of 

 a small tunnel in a steep bank of the stream showed the scori- 

 aceous base of the lava flow, resting on a somewhat baked surface 

 of gravelly clay. A fine section, about 200 yards to the north of 

 the northern wall of the Stockade, showed the basalt resting on 

 the sloping surface of the sedimentary rocks. A thin layer of 

 gravelly clay here separates the lava flow from the underlying 

 Silurian rocks. Typical features in the weathering of the basalt 

 attracted attention, and among other features noted was the 

 infiltration of carbonates of lime and magnesia from the over- 

 lying basalt for some distance into the joint and bedding planes 

 of the underlying Silurian rocks. The shortness of the afternoon 

 did not allow the party to visit the instructive example of hillside 

 runnel erosion to the east of Pentridge. — E. O. Thiele. 



EXCURSION TO EAST COBURG. 



About a dozen junior members attended the excursion to East 

 Coburg on Saturday afternoon, 4th May, arranged for the purpose 

 of studying water-action. Owing to rain havmg fallen freely a 

 couple of days before the excursion, the small streams studied 

 had laid down beautifully assorted series of sediments, which we 

 were fortunate in being enabled to see while they were yet fresh. 

 One result of the action of running water on the surface of the 

 land, we were able to observe, was how basaltic lava, which once 

 must have flowed down a valley with high land on either side, 

 exists now as a ridge with valleys on either side. The high sides 

 of the original valley, owing to being composed of more easily 

 removed material than the harder basalt of the valley, have dis- 

 appeared by water-transportation, and in their places river-beds at 

 a much lower level than the basalt now exist. The action of 

 water in carrying away from a lava plain some of the weathered 

 and decomposed lava, leaving the harder parts outstanding as 

 basaltic boulders on a boulder-strewn surface, was also studied. 

 In the tertiary deposits to the west of the Coburg Cemetery we 

 saw on a small scale a beautifully dissected plateau, with its 

 water-partings, river valleys, residual ridges, and buttes. Atten- 

 tion was drawn to the fact that all our Victorian mountain ranges 

 have been formed by denudation by the same agent as dissected 

 this piece of plateau. We saw here how rivers may destroy 

 lakes by filling them with transported material. It was pointed 

 out that the Rhone River is gradually but surely filling up 

 the beautiful Lake Geneva. No sooner is a lake formed 



