328 Transactions. — Geology. 



the crushing power of ice 3,000 feet thick, as ali-endy stated, only amounts to 

 l,227Ibs. per Ksquare inch ; thus its effect would be slight by way of crushing, 

 though there might be large erosions by the disriiption of blocks and strata 

 from their beds on the face of the mountains, whei'e 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 scoo[)ing 

 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 a 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 i-elative 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 sepai'ates 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 — tliat is, out 

 of the hills he creates new alluvial dej)osits in the plains j unfortunately, being 



