342 Glacial Period in the [July, 
from the ocean as to lower its level to the extent, I believe, 
of about 2000 feet ; and this lowering of the ocean would 
give a coast line along which the littoral mollusks might 
retreat northwards during the Glacial period. In the line 
of soundings made between Australia and New Zealand by 
the officers of the Challenger , it was found that from the 
Australian shore the water deepened gradually until a depth 
was attained of 2600 fathoms, at about one-third the dis- 
tance sccross. Nearer New Zealand the water shoaled 
suddenly, and at a distance of about 280 miles from its 
shore, a depth of only 275 fathoms, or 1650 feet, was found 
with a rocky bottom. These soundings were taken in one 
line only, and there can be scarcely a doubt that a lowering 
of the sea level 2000 feet would add more than 300 miles to 
the extension of New Zealand northward, and afford the 
necessary refuge for its fauna and flora during the Glacial 
period. 
To prove the necessity of lands to the northward, now sub- 
merged, having then been above the sea, it was not necessary 
to appeal to the evidence of the marine shells, which is so 
far doubtful, as it is known that many shallow water species, 
under other circumstances, live at a great depth ; as that of 
the inhabitants of the land was equally available and more 
certain. For the bones of the great extinbt birds are not 
confined to the drift beds, but are found in old kitchen 
middens, ovens, encampments, and other places on the sur- 
face of the glacial beds, proving, that after the cold period 
had passed away, they returned again. It is certain that 
they must have been expelled from the existing area of the 
South Island, when glaciers came down beyond the present 
coast lines on the west side, and the great plains of drift 
were being formed under water on the east. The marine 
mollusks might have passed across some channels of the 
sea, but the apterous birds required a continuous land pas- 
sage during their retreat, and the withdrawal of the waters 
of the ocean would have afforded this, not only to the North 
Island, but to the great plateau now submerged, whose 
existence has been indicated by the few soundings of the 
Challenger expedition. 
We may agree with the New Zealand geologists that 
their country stood at a higher level above the ocean than it 
now does when it was glaciated ; but instead of looking upon 
this as evidence in favour of local causes having led to the 
accumulation of the ice, it is only another link in the evi- 
dence to prove that the level of the ocean was lowered, and 
that the glaciation of the southern hemisphere took place at 
