328 T'ransactions.—CGeology. 
the erushing power of ice 3,000 feet thick, as already stated, only amounts to 
1,2271bs. per square inch ; thus its effect would be slight by way of crushing, 
though there might be large erosions by the disruption of blocks and strata 
from their beds on the face of the mountains, where gravity would also lend 
its aid. Yet, in the valley beds, as there would not be this aid, it is difficult 
to assent to such great erosions as would be required for the whole scooping 
out of the lake areas by a power equal to 12 against a resistance equal to from 
55 to 110. Hence a middle course between two opposite theories appears to 
me to be the correct one. Speaking of this geological era, the lake beds were 
there ab initio, though much modified, it may be deepened and widened by the 
action, originally of terrene, and latterly of mountain, glaciers. Thus we 
cannot give the same weight to glacial power, for erosion and transport of 
material in broad lake or valley beds composed of hard rock, as we can to the 
same power on the slopes of the mountains, or in narrow gorges, or on the soft 
tertiary formations of the coast, such as we have on the Waitaki Plains. As 
a support to this opinion I adduce a case known to you all, viz., the Water of 
Leith and Kaikorai The former, having à much larger drainage area and 
steeper mountains around it, yet passing through hard trap rocks, has but a 
very narrow valley bed ; while the latter, with a much smaller drainage area 
and low hills around it, yet passing through soft sandstone rocks, has a 
spacious valley bed. This is clearly due to the relative powers of erosion and 
and resistance; so it is with the most stupendous operations of physical 
‘geography. 
I now come to the subject of alluvial formations—a subject more imme- 
diately connected with the welfare and existence of mankind than almost any 
other—as on these are the most fertile plains and densest populations. How 
glacial action and terrace formation have to do with these will not immediately 
appear, but I hope to show they do so intimately. For a proper understanding 
of the subject—or, in other words, to grasp at one view what are very 
prolonged and diffused operations of nature—I must invite you to look at 
what is now going on, under your eyes at this present time, in many parts 
of this Province. I allude to the gold miners’ sluicing works, for by them we 
see in one day what nature commonly displays in a thousand years ; and if, in 
relation to the forces, you will agree with me that one day is as a thousand 
years, so you will admit the aptness of the illustration. 
The gold miner, in pursuing his avocations, sometimes has recourse to what 
is called sluicing—that is, washing down the auriferous strata from the hills 
into the plains—by which means he separates the gold from the gravel and 
earth. In doing this he performs, in miniature and in a few months’ time, 
what glacial action did so extensively in the course of many ages—that is, out 
of the hills he creates new alluvial deposits in the plains ; unfortunately, being 
