509 
The snow rivers are tlLO.se , by the action of which the surface 
of the plains has derived its present form. In their passage through 
the mountains they carry with them the desintegratod materials 
they meet with. These are of every variety of size, from impal- 
pable mud to large boulders; they are deposited along the beds of 
the streams, the heaviest particles highest up and the remainder 
over the whole length to the sea. Thus the beds of the streams 
become built up to, and above the level of the already illdefined 
banks ; the waters leave the old courses and cut out new ones ; 
these they rapidly widen till the water spreads and rambles over 
miles in width , and again deposits the materials brought down. 
Each stream thus roams over a large area , its various courses radiat- 
ing from a centre at or near the gorge through which it debouches 
on the plains. It builds up , by layer on layer, that portion of 
the plain which it is destined to work over, and is ever thus tra- 
velling from north to south, and south to north, over a distance 
averaging about forty miles. It thus leaves within its field of opera- 
tions a nearly level surface, slightly corrugated in lines radiating 
from a centre, and closely resembling a lady’s fan, by which name 
it has been most appropriately designated in Dr. Haast’s report. 
This operation has been in action since the pleistocene period, and 
no doubt, the present rivers repeat simply on a smaller scale the 
action of the large pleistocene torrents which formed the upper part 
of the plains. The present rivers have, in consequence, according 
to their present size and position of sources cut more or less deeply 
into the old fans at the foot of the mountains, whilst they raise 
their beds at a greater distance from the mountains and forme there 
the new fans near the sea coast. Thus , the river beds themselves 
rise from the sea to the mountain gorges at a tolerably regular 
slope of from 20 to 30 feet per mile; running from the gorges 
between terraces of great height, which gradually diminish until 
they die away altogether, leaving the rivers to run on the sur- 
face of the plains for a short space, after which they begin, instead 
it. The depth of the bore-holes in the streets of Christchurch averages about 83 feet 
and the water rises to about 10 feet above the surface. 
