330 Traiisactions . — Geology. 



This led me to enquire if there was a law of deposit, and, in going over all 

 the surveys and levels to be obtained in this Province, I found that all were 

 more or less deficient in completion, excepting the very careful survey of the 

 Taieri Plain by Mr. Adam Johnston. Here the information was as complete 

 in every respect as could be desired, though the extent of deposits are very 

 small in comparison with those of the Canterbury livers. However, the 

 essentials were the same, viz., alluvial deposits spread out over a plain from a 

 narrow gorge in mountains running parallel with the plain. Thus the deposits, 

 as brought out, had free scope for extension over 180 degrees of the horizon, 

 and the result is precisely that of what may be seen in the " tailings" of many 

 of our gold workings. The Taieri, bearing the debris from mountain glaciers 

 originally, and now that of floods, issues on the plain at Outi-am Bridge, and 

 meets the low-water mark of the tide at Adams', a distance of 12^- miles 

 measured by the sinuosities of the channel. The difference of level between 

 the river, in its ordinary state, at Adams' and Outram Bridge, is 17 "5 7 feet ; 

 and the levels of intermediate distances are given respectively, showing a curve 

 of a very decided contour. The curve is neither that of the hyperbola nor 

 circle. With the data given, and by the formula already used in given cases, 

 it was compared by computation with the parabola, but found not to accord 

 therewith. It was then tested by the properties of the ellipse, with the 

 following result, so nearly approximating that it may be said to be one and 

 the same : — 



At Outram Bridge 



At intermediate points 



At Adams' Accommodation House. 



Thus, in this instance (and I have no doubt the agreement will be the same 

 in all similar conditions of water scooping out the gravel, clay, and mud), water 

 descending to its level, through alluvial soil, digs or scores out its bed to the 

 curve of the ellipse ; and thus, in a remarkable manner, imitates the semi- 

 liquid glacier in its operations on the valleys of the earth. 



This, then, is the law of erosion, but not of deposit, the next subject of 

 enquiry. In searching for a law of deposit we again refer to Mr. Johnston's 

 survey, which gives us ample data. Taking his levels between the same points, 

 we find the distance by flood-channel 59,730 feet, or about 11 miles ; and the 

 difference of level 30 feet. Levels are also given at intermediate points, 

 resulting in a decided curve. In this case the summit of the alluvial banks 

 are taken, the effect of many floods, and not of one in particular; as 

 Mr. Johnston's map elicits the curious fact that separate floods have very 



By Ellipse. 



By Survey. 



Differences. 



. 00-00 . 



.. 00-00 



... 0-00 



• 11-55 . 



.. 10-75 



... 0-80 



U-12 . 



.. 13-26 



... 0-86 



15-06 . 



14-95 



... 0-11 



17-12 . 



.. 16-78 



... 0-34 



. 17-57 . 



.. 17-57 



... 0-00 



