GLACIAL GEOLOGY OE COIMADAI. 
329 
Messrs. Sweet and Brittlebank, in the paper already referred to, 
state that in their opinion the glacial conglomerates were deposited 
under water by the agency of floating ice near shore, and that their 
final arrangement is due to u moving waters.” They state that their 
conclusions are in agreement with those formed by the officers of the 
Geological Survey of Victoria on this point, but we have been able to 
find very little in the writings of such officers which will throw much 
light on the statement of Messrs. Sweet and Brittlebank. 
Mr. E. J. Dunn, F.G.S., writing of the Derrinal beds, states : — 
“ Icebergs that started their career as glaciers alone would account for 
the phenomena presented by this conglomerate. The glaciers would, 
while gliding down their native valleys, accumulate in their mass vast 
quantities of earth, sand, clay, stones, pebbles, and masses of rock 
from the sides of the valley, and from the branch valleys running into 
it. A s they pushed out into the ocean or lake, they would become 
detached, and were then driven by wiud and current to the site of the 
present conglomerate. As they floated over or became stranded, the 
melting of the ice would set free the included rocky or earthy matter, 
which would fall to the bottom, and just in such a manner as sections of 
the conglomerate expose.” That icebergs did become stranded over 
the Derrinal area is shown, according to Mr. Dunn, by the mass of 
bed-rock (christened Dunn’s Rock by Professor Spencer) planed and 
scored in Lot A20, parish of Knowsley. Without inquiring whether 
Messrs. Sweet and Brittlebank rely, with Mr. Dunn, on icebergs to 
account for the smoothed and grooved appearances of the bed-rock, their 
explanation of the phenomena appears to involve the conclusion that 
not only the included stones but also the matrix of the conglomerate 
was carried from the land by icebergs or floating ice ; that the 
berg, either before or after stranding, parted with the material it was 
conveying, and that this material, after being deposited, was finally 
arranged by “ moving waters.” 
With respect to the smoothed and grooved surfaces of the bed- 
rock — of which a large number of instances have now been reported — 
there does not appear to be any good reason why the well-established 
theory of their glacier origin should be departed from. The action of 
icebergs is in general attested by the crumpling and crushing of 
strata rather than in the smoothing and polishing of their surfaces ; 
and there is less difficulty in believing that, when the glaciation was 
at a maximum, either the ice-sheet or a local glacier passed over the 
surfaces in question — smoothing, polishing, and grooving them — than in 
endowing icebergs with physical properties which, so far as experience 
shows, they do not possess. 
But if it is difficult to picture an iceberg forsaking it s usual 
practices and smoothing instead of crushing the rocks it strands upon, 
it is still more difficult to imagine icebergs drifting from the ice-sheet, 
and either parting with their included and adherent material with such 
mathematical accurac} r as to form well-marked strati tied beds traceable 
over a large area of country,* or parting with it in such a manner that 
after its deposition it could be arranged by “moving waters” in stratified 
beds. 
We are of opinion that after the maximum extension of the ice- 
sheet a subsidence of the land now covered by the glacial beds took 
place, followed, probably, by several oscillations of level. Into the 
