DOBSON AND SpeiGHt.—So-called “ Railroad” at Rakaia Gorge. 629 
which it crosses. The rise from the river over the first terrace noted by 
t is, in our opinion, somewhat delusive, and is due to the eee 
formation of dunes in an approximate line with the edges of the depression. 
Finally, there is à point which must be noted as to variations in width— 
viz., the presence of a number of contractions due to reductions arranged 
in rectangular steps. These are excellently shown aca на, line of the 
depression edges away on climbing the terrace 
The possible explanations of the origin of dis tha базлар каше which 
should be considered are as follows :— 
. It is an old stream-bed. This is ruled out of consideration on account 
of the rising grade on meeting ө, кг pee (see Plate 65, fig. 2), and 
also on reaching the slopes of Brya 's Hill. 
2. It is the bed of a glacier. If this i is so the phenomenon is unique ; but 
there are insuperable objections against this explanation. The side levees 
are, agone: to Haast, old vigere moraines, but they are composed almost 
entirely, even acco to wn showing, of fine material, and are not 
. formed of the angular lida: Eli constituting moraine. Then, again, 
it is difficult to imagine the precise method by which a glacier eroded such 
are formed е stream-action in an area мл which the ice had орге: 
and they are to be attributed entirely to the work of streams from 
the ice-front as it retreated up the valley. Had they been pi gsdal they 
could not have survived in their entirety the erosive action of the great 
glacier which passed over the ground between Mount Hutt and the Rock- 
determin ined, and, in in any а и the objections made to the glacier arse rad 
will hold good even if the advance was of minor importance. If, then, the 
terraces are post-glacial, the туы ыйга must be post-glacial and cannot 
be credited to ice-action. 
3. It is due to wind-action. While admitting that wind is responsible 
for certain features, one cannot credit wind with forming an excavation 
with subparallel sides, three miles in length, and cut out of terrace-gravels, 
and perhaps out of underlying rhyolite. Although this rock is not visible 
in the floor, yet it certainly lies at a shallow depth, judging from the 
neighbouring exposures, and it may be cov vered by a thin veneer of loose 
4. It is due to faulting. According to this explanation it may represent 
an agra stt such as can be seen near Glen Wye, on the upper Waiau 
River (see McKay, of Geological Explorations for 1890-91, p. 16). 
If this explanation is correct, the depression can be attributed to trough- 
faulting. This will explain the long subparallel margins, and the rectangular 
modifications of width can be regarded as due to fault splinters of the main 
fault-line. Although we think this explanation the most satisfactory, we 
have arrived at it largely by the method of exclusion, and not viri there 
is positive evidence of faulting along the line. Evidence of dislocation was 
looked for where the upper end terminates on a high cliff-like bk: red 
