254 JOURNAL OF SCIENCE. 
period than they are now,* and the evidence he brought for- 
ward has been admitted by all. For, example, there is no 
doubt but that at one time, not geologically remote, the 
glaciers of the Waimakariri and of the Rakaia reached the 
Canterbury Plains, and that a branch from the Upper Rakaia 
passed through Lake Heron and joined the glacier coming down 
the Rangitata. This former great extension of our glaciers has 
been aptly called by Dr. von Haast our “ Glacier Epoch,” to dis- 
tinguish it from the “ Glacial Epoch” of Europe, with which 
probably it had no connection. But we have evidence of an- 
other and much earlier glacier epoch than the one just men- 
tioned. At Lawrence, in Otago, there is a small rock-basin 
filled up with a conglomerate, the stones of which have come 
from the west, and some of them are distinctly marked by gla- 
cial strie. ‘This conglomerate can be traced in a south-east 
direction to the Tokomairiro Plains, proving that a glacier at 
one time descended a valley running from the Tapanui Moun- 
tains to Kaitangata, quite across the present drainage of the 
country. The lower part of this valley has been filled up with 
rocks of oligocene age, and we have here, therefore, the 
proof of an eocene glacier epoch.f At Wharekauri, or 
Big Gully Creek, in the valley of the Waitaki, there is 
also another rock-basin filled with oligocene rocks. And at Castle 
“Hill, on the road from Christchurch to Hokitika, there is evidence 
of a third and still earlier glacier epoch in a rock-basin, some 
eight miles long, which has been partly filled by marine upper 
cretaceous rocks, upon which lie oligocene and miocene strata. 
What now has been the cause of these three glacier epochs 
in New Zealand? Are we to attribute each of them to a 
general lowering of the temperature of the southern hemisphere 
—that is, to a true glacial epoch? Or are we to refer them to 
some other cause? According to Mr. Wallace our last glacier 
epoch was due to a general lowering of the temperature, brought 
about by changes in the eccentricity of the earth’s orbit, in com- 
bination with geographical changes, as explained by Dr. Croll. 
It will therefore be necessary to say a word on this subject. 
It is well known that, owing to the varying attractions of the 
planets, the mean annual velocity of the earth in its orbit is not 
the same year by year; and as the earth has to complete its 
annual revolution round the sun in a fixed time, the distance it 
travels in each year varies. When the mean velocity increases 
the orbit increases, and wice versa. But as the length of the 
major axis of the orbit must remain constant, a greater or less 
length of orbit is obtained by an increase or cecrease of the 
minor axis. So that when the average speed of the earth is 
great the orbit becomes more nearly circular, and when the ave- 
rage speed is small the orbit becomes more oval. But the sun 
must always occupy one of the foci of the orbit. Therefore as 
* Notes on the Geology of the Province of Canterbury, Cant. Pro, Gov. 
Gazette, 24th Oct.. 1862, 
T Geology of Otago, p. 93, and Cox, Geol. Reports 1878-9, p. 47. 
* 
ng te 
