410 . Transaction?'. 



periods. Only after long-coiitiniied observations will it be possible to isolate 

 the various anomalies and refer each to its exact cause. This line of inquiry, 

 therefore, gives at present little satisfactory result except in so far that a 

 recent rapid retreat must be granted, but whether this retreat is periodic 

 or not is quite uncertain. 



There is geological evidence of a dry climate obtaining over the region 

 in question either contemporaneously with the extension of the glaciers, 

 or somewhat subsequent to it, in the fact that the loess which so completely 

 mantles the country was a rock-flour carried by wind from the river-beds 

 of glacial rivers. This is the general opinion of its origin, although Captain 

 Hutton maintained that this same deposit was a marine silt. It probably 

 indicates that the conditions over the east coast of this Island resembled 

 somewhat those which occur in Thibet at the present time, only they 

 are not so pronounced. A reference to this probable steppe climate will 

 be made later when mentioning the xerophylly of certain New Zealand 

 plants. 



Further conclusions may be based on the examination of the terraces 

 which characterize the valleys of nearly all the rivers of New Zealand. 

 Hutton attributed these almost entirely to a recent rise of the land giving 

 all the rivers increased power of corrasion. In a paper on " The Terrace- 

 development in the Valleys of the Canterbury Rivers " (Trans. N.Z. Inst., 

 vol. 40, 1907) I have given my reason for thinking that, as far as Canterbury 

 is concerned, the major movements have been downwards since glacier 

 times, and that unless the land has been differentially elevated quite recently 

 along an axis almost coincident with the main range, or closely parallel 

 with it, mere elevation cannot account for the characteristic features of the 

 terraces. In that paper I urged the importance of the falUng-off of the 

 supply of waste owing to the lowering of the land, thus giving the rivers 

 increased power of corrasion, as the principal cause for their occurrence. 

 I have since seen reason, based on wider observation, to modify this opinion. 

 While admitting the necessity for attaching greater importance to the supply 

 of waste, and recognizing its great influence in the case of the large rivers 

 of Canterbury, there are numerous terraces which cannot be attributed 

 to that cause. Observations made recently on the small fans of detritus 

 in the dumping-grounds of mining claims confirm my opinion that they 

 are built up chiefly when the supply of water and its accompanying load 

 of waste is plentiful, but that, when the supply of water is diminished, ter- 

 racing of the fan immediately results. The profile of these terraces repro- 

 duces exactly those which occur on our large shingle-fans, and also those 

 formed by the rivers which cross the Canterbury Plains. The inference 

 seems, therefore, that the material of our river-terraces was brought down 

 in a pluvial epoch, and terracing commenced actively when the supply of 

 water began to fall off. This course does not aflect the principle that supply 

 of waste is also an important factor affecting the formation of terraces. 

 The condition of many of our Canterbury streams at the present time, when 

 deposition is overtaking transportation in the lower portions of their courses. 

 is evidence that a maximum of erosion is past and another cycle of deposition 

 has commenced. This may be due to the lowering of the land, but it may be 

 due to a change in the supply of rain or to alteration in the climatic con- 

 ditions. 



These are the chief lines of evidence of purely geological character 

 which are connected directly with the question, but there are others of bio- 

 loyical character which must b(> considered. The first of these concerns the 



