388 Lake Wakatipu, New Zealand. [July, 
is a limited deposit of tertiary limestone, containing as fossils, 
Ostrea Wullerstorfii, Cucullea alta, C. Worthington, Panopea 
plicata, and many others. The junction of the limestone with 
the crystalline rocks beneath can be seen but a few feet below 
the surface of the lake. The limestone being at the present level 
of the water, the valley must have been eroded to that depth 
before the limestone was formed. As its deposition took place 
beneath the waters of the ocean, the valley was at one time an 
arm of the sea, and was afterwards upheaved to its present eleva- 
tion or higher, and the wearing down of the valley continued. 
We have, therefore, as the sequence of events that resulted in 
the formation of Lake Wakatipu, the following : — 
(1.) The Southern Alps forming a sloping table-land, the 
highest remaining point of which is Mt. Cook, 13,200 feet above 
the sea; on this high table-land were deposited immense amounts 
of ice and snow, brought by the warm, moist winds from the 
ocean, which formed the glaciers that flowed off in various direc- 
tions towards the sea. One of these ancient rivers of ice had its 
source in the region about Mt. Earnslaw, — which, however, was 
then greatly different from its present form — and flowed over 
what is now the valley of Lake Wakatipu. This old-time glacier 
continued its slow motion towards the sea for unknown ages, 
until it had ground out the solid rock to a depth of five or six 
thousand feet in vertical thickness, and for over a hundred miles 
in length. 
(2.) The work of this mighty glacier was finally terminated 
by a sinking of the land, which caused the valley to become an 
arm of the sea, similar in every respect to the deep, narrow 
fiords that form such a characteristic feature of the west coast of 
New Zealand at the present day. What before was an alpine 
valley filled with hundreds of feet of ice then became the home 
of huge oysters, and many other forms of marine life, whose re- 
mains we now find in the limestone. We know that the sea 
filled the valley for a long time, since the compact gray lime- 
stone that it left behind it was not formed rapidly, as sandstone 
and conglomerate may be, but the material was first gathered 
from the waters to form the shells of mollusks and foraminifera, 
or the hard parts of corals, crinoids, etc., and then these worn 
down to a fine detritus by the waves and spread out as à calca- 
reous sediment, before the hardening process of rock-making Can 
commence. Together with the limestone are beds of fine shale 
and masses of conglomerate, composed of both rounded and angt- 
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