342 Transactions. 



once by a large glacier which flowed south-west, as evidenced by the 

 .smoothed slopes of Fighting Hill near its junction with the Rakaia. The 

 outlet of the valley is very wide and open towards the Rakaia, but it is 

 partially blocked by a large moraine, partly a terminal of the glacier which 

 issued from this valley, and partly a lateral of the main glacier. This 

 ponded back a large lake in the basin once occupied by the glacier, which 

 .secured an outlet not by the Rakaia, but by the Selwyn Valley — a result 

 no doubt aided by the active erosion of the latter stream, which enabled it to 

 cut back its head through the range of foothills and to draw on the basin 

 in the rear. The existence of this lake is demonstrated by the deposit of 

 glacial silt which occupies a part of the floor of the emptied basin near the 

 High Peak Station. The Selwyn now flows from the valley through a 

 narrow gorge of more recent date than its upper basin, and it has gathered 

 to itself all the drainage belonging to this basin M^hich once added to the 

 Rakaia. The Rakaia Glacier has thus been directly or indirectly responsible 

 for several remarkable changes in the drainage directions in its basin and 

 those of its immediate neighbours. 



8. ToTARA Forest. 



A very striking feature of the Upper Rakaia Valley is the forest, com- 

 posed chiefly of totara {Podocar]ms Hallii), which clothes the hillsides for 

 miles on the north bank of the river, and which occurs in large patches 

 ■on the southern bank (see Plate VH, fig. 1). In this locality the wet 

 westerly winds reach well across the main divide before they become 

 parching and dry with the usual characters of the Canterbury north-wester, 

 and the mountain ranges on the south of the Rakaia shelter the upper part 

 of the valley from cold southerlies ; so that the conditions are thus favour- 

 able to the growth of this rain-forest tree. The patch iii the Rakaia is but 

 the remnant of an ancient forest containing totara which extended over a 

 wide area on the eastern side of the range, and reached southward through 

 the Mackenzie country into Central Otago, the important bearing of which 

 ■on the question of post-glacial climates is considered by the author in another 

 paper in this volume. Further details regarding this plant formation will 

 be found on page 363. 



PART II.— PLANT ECOLOGY. 

 By L. Cockayne, Ph.D.. F.L.S., and R. M. Laing, M.A.. B.Sc. 



[Head before the Philosophical Institute of Canterbury, 5th October, 1910.] 



1. INTRODUCTION. 

 Very little has been published regarding the botany of the Rakaia, 

 Ashburton, and Rangitata Valleys and the mountains adjacent. Sir Julius 

 von Haast* made considerable collections of the plants during his early 

 explorations in 1861, 1864, 1865, and 1866 (Haast, 1879), and these were 

 determined by Sir Joseph Hooker, the new species being described in 

 the " Handbook of the New Zealand Flora." while the rarer species are 



* In his first expedition Haast was accompanied by Dr. A. Sinclair, who was, 

 unfortunately, drowned in the Rangitata River, falHne, as Haast write.«, " a \ictini to 

 his zeal for his chori.shcd science." 



