Horron.—On the Last Great Glacier Period in N. Z. 385 
Cassis that is found in the upper series, Ancillaria australis, two species of 
Cladopoda one of which is still living, Zmperator imperialis and Rotella 
zealandica, showing that here also we cannot call to our aid any great 
diminution of temperature. We have no marine deposits in New Zealand of 
older-pliocene date, for, as I shall subsequently show, the land then stood at a 
much higher level than it does at present, consequently we have no proofs 
here, either one way or the other, of a change of climate, but as the elevation 
of the land would, if high enough, be able by itself to account for all the 
phenomena, there is no necessity for calling to our aid any other cause. 
During miocene times our climate was warmer than at present, as is proved 
by fossils of the genera Conus, Mitra, Marginella, Crassatella, Limopsis, 
Perna, and the large species of Cucullea and Cardium which then inhabited 
our seas. * 
We must therefore necessarily infer that the greater extension of the 
glaciers was caused by greater elevation of the landt, and their subsequent 
reduction in size was caused by subsidence, and so far Dr. Hector, Dr. Haast, 
and myself agree. Dr. Hector, however (“ Jour. Roy. Geograph. Soc.,” 1864, 
p. 103, and’ Geo. Mag.,” 1870, p. 70), and Dr. Haast (“ Cant. Plains,” p. 14, 
and “Quar. Jour. Geo. Soc.,” XXI., p. 131) appear to attach considerable 
importance to the erosion of the vallies by the glaciers reducing the area of 
land above the snow line. This appears to me to be an unnecessary and 
exaggerated view of the rapidity of glacier erosion}, and the fact that eocene 
or miocene marine rocks are found far up many of these vallies, such as at 
the Rakaia, Canterbury, and some twelve miles above Queenstown in Lake 
Wakatipu, proves beyond dispute that they had attained to nearly their 
resent size in eocene times. Dr. Hector also assumes (Zràns. N.Z. Inst., 
IT., p. 373) that the chief erosion, by which the vallies are eaten back by thé 
glaciers, takes place at the abrupt fall known as the “ice cascades.” But the 
friction, and therefore the power of erosion, of any solid body like ice must 
vary as the cosine of the angle of inclination, and consequently the greater the 
slope the less the erosion. The maximum of erosion must necessarily be at 
the upper angle of the ice cascade, where the ice bends downward by its own 
weight, and consequently the effect would be the gradual reduction of an 
abrupt fall to one of gentle inclination, and this is fully borne out by the fact 
* This is the usual paleontological argument, but I believe that, when applied to 
extinct species, it may lead to very erroneous deductions, and that when opposed to 
physical arguments it is of no weight at all. 
+ An elevation of from 2,000 to 3,000 feet would be sufficient to account for all the 
phenomena, while an elevation of 550 feet would connect the two islands. 
$ On this subject see an excellent paper by the Rev. T. Bonney in the “ Quar, Jour. 
Geol. Soc.,” 1871, p. 312. 
yi 
