164 Proceedings of the Royal Society of Victoria. 



3, but much smaller than the average size of them. Towards its 

 eastern margin there is a dyke or plug of basalt having a width 

 of about 6 feet in the cliff, and a N.W. and S.E. bearing. In 

 the flat to the south-east two drains reveal a dyke of basalt 10 

 inches wide, having the same general bearing as that in the cliff. 

 Probably it is the southerly extension of that dyke. This basalt 

 is a hard, dark blue, dense rock, much like that in the plug in 

 Neck 3, and it contains amygdules of calcite and patches of 

 green olivine. It weathers a grey colour like that of the soil 

 from the Jurassics, and can be traced up the cliff for some 2^- 

 chains. The latter part of its course is through Jurassic strata, 

 the former through tuff. It is probably somewhat younger than 

 the tuffs of the neck, though practically contemporaneous with 

 them. 



Packed up against the foot of the cliff, here about 30 feet 

 high, are blocks of a dense, hard, coarse olivine basalt, and a few 

 loose pieces of agglomerate thrown out of drains on the flat. 

 The olivine occurs in patches over 1 inch in diameter. It is, 

 therefore, probable that the neck extends for some little distance 

 into the flat, where it may partake more of the character of 

 Neck 2. 



The tuff of this neck difters from the ordinary tuffs of the 

 district. It has more of the character of a friable, granular, 

 rather incoherent clay, and contains numerous grains of quartz 

 sand. It induces the belief that it consists of a mixture of 

 sedimentary and volcanic material, and this it probably is. The 

 absence of a greater proportion of sand grains may be explained 

 by supposing most of the visible material to be a mixture of 

 Jurassic mudstone in a pulverised state, with volcanic dust or 

 fine tuff. 



Other Local Volcanic Occurrences. 



In addition to the basalt showing within the boundaries of the 

 volcanic necks, there are several other occurrences of this rock 

 among the Jurassic strata. Three of these occur close together, 

 between G and 8 chains north-east from the northern end of the 

 jetty. The most easterly one is a dyke of basalt, 6 inches wide 

 and about 20 yards long, having a N.E. bearing. The rock is a 

 dense black basalt of fine texture. 



