HuTTON. — On the Last Great Glacier Period in N. Z. 385 



Cassis tliat is fouud in the upper series, Ancillaria australis, two species of 

 Claclopoda one of which is still living, Imjyerator imperialis and Rotella 

 zealayidica, 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 lai-ge species of Gucullcea and Gardium 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. Hoy. Geograph. Soc," 1864, 

 p. 103, and "Geo. Mag.," 1870, p. 70), and Dr. Haast (" Cant. Plains," p. 14, 

 and " Quar. Jour. Geo. Soc," XXL, 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 E-akaia, Canterbury, and some twelve miles above Queenstown in Lake 

 Wakatipu, proves beyond dispute that they had attained to nearly their 

 present size in eocene times. Dr. Hector also assumes {Trans. N.Z. Inst., 

 IL, p. 373) that the chief erosion, by which the vallies are eaten back by the 

 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 paleeontological 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. 



f 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. 



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