00-0 



00-0 



0-0 



13-3 



14-4 



1-1 



19-1 



19-5 



0-4 



23-2 



22-7 



0-5 



25-7 



26-1 



0-4 



30-0 



30-0 



0-0 



Thomson. — Glacial Action in Otago. 331 



unconforming levels at different parts of tlieir courses. This ciu've of deposit, 

 as I may call it, was first tested by the properties of the ellipse, but found not 

 to accord ; it was then tested by the parabola, with the following results : — 



By Parabola. By Sukvey. Differences. 



At Outram Bridge 



At intermediate points 



At Adams' Accommodation Hoiise . 



' Thus, the curve of deposit may be said to be identical with the parabola, 

 varying from it, in a course of eleven miles, on an average of six-tenths of a 

 foot. The theoretic course of a cannon ball is in a curve of the parabola, 

 subject, as it is, to unequal resistance and deflection of the atmosphere and its 

 currents ; it, in practice, does not excel water in its mathematical truth, as 

 here displayed. 



Here, then, are two laws proved in the Taieri " tailings," as the gold digger 

 would term them. The law of scooping out is as the ellipse ; that of spreading 

 out as the parabola. And what practical objects do these lead us to. Many, 

 no doubt, will develop themselves in various minds ; one or two I may shortly 

 state. 



The first is one of geological interest. When the plains were being covered 

 by detritus to the parabolic curve, glacial action was, of necessity, in full 

 force. The valleys were filled with moving ice and turbid water, grinding 

 against the sides and bottom of the earth. At the time this was in process 

 the torrents issuing on the plains would have no more certain beds than the 

 sluice waters of the miner, but would diverge to and flow over 180° of the 

 horizon, depositing its "sludge" where there was readiest outlet or lowest 

 level. 



But as the cycle pursued its coui'se, so, with the increase of temperature, 

 the ice of the glaciers would melt or retreat in diminished bulk to the tops of 

 the valleys ; then the depositing power would virtually cease, and the opposite, 

 or eroding action, by the torrents finding for themselves a confined channel, 

 would take place. Thus we arrive at the present era. As it is with great, 

 so it is with small, things. No sooner are the miners' claims worked out than 

 deposits, spread out in the parabolic curve, cease, and the clear water, now 

 unused, seeks for itself a confined channel in the elliptic curve. 



The other question may be called an engineering one. If detritus is 

 deposited as the parabola, and scooped out as the ellipse, then we may conclude 

 that such rivers as the Waitaki, on whose outlet the sea is encroaching, will 

 more and more adhere to a confined channel — the elliptic curve following a 

 lower course than the pai-abola ; but that such rivers as the Waimakariri, 



