450 PROCEEDINGS OF SECTION GC. 
sub-aérial. Even there, it is probable that the ashes and scoria 
ejected soon raised a mound, which rose above the waters, while 
the lava continued to well out and spread for a long distance on 
the sea bottom. 
While speaking of the igneous rocks of the district, I may 
briefly refer to the singular obsidian bombs, which are so frequently 
picked up. They have been gathered in the drifts near Portland, 
on the surface of the basalt at Hamilton, and in the Byaduk 
Creek, near Mount Napier. But, curiously enough, they are also 
found in ironstone gravel at Harrow, amongst the dééris of 
metamorphic rocks at Balmoral, and very abundantly on the mud 
plains to the north of the Glenelg. There are not now any signs 
of volcanic rocks very near the last-mentioned places, so that the 
origin of the bombs is somewhat of a puzzle. They vary in size 
from }inch to 1} inches in diameter. The smaller ones are flattish, 
and look much like black buttons, but the larger ones are thickerand 
almost basin-shaped. Boat-shaped, and even amorphous, pieces are 
not rare, and a very fine elongated specimen was once shown to 
me, which was said to have been found near Lake Wallace. No 
doubt they have been carried about the country by blacks, who, as 
is well known, prize them highly, but those found near the 
Glenelg river must, from their comparative abundance, be near 
the source whence they were derived. That they have not been 
carried far amongst drifts is evident, since they are seldom, if 
ever, waterworn. The only explanation which suggests itself to 
me, is that they have come from some small volcanic vent in the 
neighbourhood, which is now concealed by waste material from 
adjoining rocks. 
The dune limestone, which has been incidentally mentioned 
before, is not a very important formation ; but, from its bold, 
striking character, it has attracted a good deal of attention, and 
has been described by more than one writer. The late Rev. J. T. 
Woods confounded it with the Pliocene crag of Suffolk, and 
attributed it to the action of ocean currents. In one of his later 
publications, however, he frankly acknowledged his mistake, and 
gave the true explanation of its origin, viz., the action of wind 
upon the sand washed up by the waves. In the course of his 
remarks he says :—‘“ Professor R. Tate, who first asserted the 
formation to be AXolian, found small shells in portions, and these 
were land shells—not marine, and of the kind now existing 
on the coast. When I first saw this deposit I imagined it 
to have been derived from marine currents ; but a better know- 
ledge of the floor of the ocean shows us that marine currents do 
not leave such stratification. Besides the land shells, and the 
fact that the strata show no signs of upheaval, I found in subse- 
quent years, by various sections on the coast, that this deposit is 
only an indurated portion of the sand-dunes with which it is 
always associated. It is an aérial rock, and is stratified by the 
