GLACIAL PERIOD. 217 
wall, and the few survivors, except Fuchsia and some others, would 
be confined to the summits of the hills, faces of rock, and such other 
stations as offered tolerable conditions—similar stations, indeed, to 
those occupied even yet at low levels by certain alpine plants. The 
species of the lowland forest would not be decimated, for on quite 
small islands at the present time there is a rich forest flora. 
Next, as the years passed by in their millions, the land once 
more slowly rose, and fresh immigrants probably came from the north, 
the south, and the west. Then, quite recently in its geological 
history, but really an extremely long time ago, owing either to a 
change of climate or to rising of the land, or probably to both causes, 
there came a period when great glaciers filled most of the river-valleys 
of the South Island, some even extending to the Canterbury Plain. 
In the North Island the glaciation appears to have been confined 
to the subalpine and alpine belts (fig. 98), where it still remains 
on the summit of Mount Ruapehu. The increased height of the 
Southern Alps would lead to a drier climate on the east than at 
present exists, so that the species of the adjacent lowlands would 
either perish or move to where conditions were more suitable, or 
through their innate plasticity assume forms more resistant to 
drought. Evidently no few of them did so. The evidence for this 
opinion has been already told in the story of the kowhai (Sophora 
microphylla). It is revealed, too, by the behaviour of those other 
trees which at an early stage of their career are drought-tolerating 
shrubs, but which later become ordinary trees. Such show most 
clearly the impress of two different environments, neither of which 
stamps its impression with an indelible stamp. As the glaciers 
slowly retreated much bare ground would gradually become available 
' for recolonization. Seeds from plants of the lowlands, and. from 
plants of those rocks and peaks which projected above the ice, 
would be carried to this bare ground. Some would germinate, and 
in course of time a plant population suitable for the new state of 
affairs come together. Some of these plants would be ancient enough, 
though many archaic types must have perished ; others would have 
slowly been evolved under the new conditions. Thus has possibly 
come about that extreme diversity of form shown by Veronica, 
Celmusia, and other genera, and it may be that much of the high- 
mountain flora is of quite recent origin. Many of the species of the 
New Zealand flora must be of recent origin—indeed, species-making 
must be still in progress. 
