Hurron.—On the Lower Gorge of the Waimakariri. 458 
firstly, because there are no traces of terraces between the Gorge Hills and 
the margins of the plains; secondly, because having once cut the col the 
river would be held there by the hard rocks on either side exactly as it is 
held now ; and, thirdly, because in order to remove the shingle-beds above 
the present level of the plains, the river must have first filled up the col 
with gravel to at least this height before it left the col, and there is no 
evidence of its having done so ; the highest terrace inside the col being only 
148 feet above the river-bed. Consequently the river can never have left 
the col since it first excavated it, and it is therefore impossible that the 
river could have removed the missing gravel beds on each side. 
If now we take the only other possible view; that is, we suppose— 
although there is no evidence in favour of it—that the col was formed by 
some other agency than the river, which merely filled it and the surround- 
ing plains to their present level; and then, happening to run through the 
col when it commenced cutting down—which is very improbable—it formed 
the present gorge. If we take this view then we shall not be able to ex- 
plain, first, how the river could deposit flat beds of shingle, some ten miles 
wide, between Sheffield and Oxford ; nor, second, can we explain the origin 
of Racecourse, and Little Racecourse Hills, and the gravel beds round the 
eastern base of the Malvern Hills; which are shown by the form and 
arrangement of the materials composing them not to be portions of old 
moraines, although Little Racecourse Hill contains re-arranged morainic 
matter. Neither of these hypotheses will explain the facts. If we suppose 
that the col was cut by the river, large masses of gravel must have been 
removed without any apparent cause. If we assume that the river did not 
cut the col, then we cannot account for the gravel hills rising above the 
plains. Evidently river action alone cannot explain the whole of the 
_ phenomena. 
The following is my explanation :—The shingle brought down by the 
rivers not only formed the present plains, but accumulated to a thickness of 
some 50 or 70 feet higher than at present. At this time Gorge Hill pro- 
jected above the shingle, but Little Gorge Hill and a large portion of the 
spur between the two were buried. The river, swaying about in the plains 
between Oxford and the Gorge Hill, was arrested in its southerly swing by 
the latter, and then, running along the north-easterly base of the hill over 
the spur, it cut down through the gravel beds into the rocks and formed the 
col. A period of general subsidence of the land followed, during which the 
river partly filled up the col again with shingle, but at length, the depres- 
sion still going on, the sea reached, and passed, this portion of the plains, 
Sweeping away the upper 50 or 70 feet and reducing all to a common level, 
except the Racecourse Hills. The col, remaining as the estuary of the 
