Speight. — TJw Post-glacial Climate of Canterbury. 419 



baluiice which exists between the struggling elements of different plant 

 associations. It seems, therefore, that a slight desiccation of the climate 

 can be inferred from the restriction of this forest. The disappearance had 

 in all probability begun before the arrival of the Maori, following on a period 

 of drier climate after a moist period which favoured its growth. The 

 forests would then be specially subject to the action of fire, except in those 

 places favoured by moist conditions. Fire certainly aided in their destruc- 

 tion, but it is improbable that it was wholly responsible for it. 



The present conditions are decidedly dry over a large tract of country to 

 the east of the main range ; however, this is due )iot altogether to lack of 

 rail), but to the influence of parching winds. Under the combined influence 

 of these two agents the vegetation is now markedly xerophytic, but when the 

 plants are grown in a moist and still atmosphere they readily reveii; to leafy 

 forms, as has been proved by the experiments of Dr. Cockayne on the wild- 

 irishman {Discarid toumatou) ("The New Phytologist," vol. 4, p. 79, 1905). 

 Dr. Cockayne has suggested to me that this readiness to revert to the leafy 

 form may be due to the fact that at some period anterior to the present 

 somewhat dry one the prevaihng climatic conditions were moist, and that 

 owing to the environment the tendency to become more or less permanently 

 xerophytic was checked, and the ability to respond quickly to a moist 

 atmosphere has been kept latent up to the present time. 



I am aware that this evidence is not convincing, and that it is merely 

 sufficient to establish a prwia facie case for consideration. If, however, 

 the conclusion that a rainy climate succeeded the last glacier maximum 

 over a wide area to the east and south-east of the Southern Alps be 

 accepted, the reasons for such a change may be briefly considered. 



This moist climate may be attributed to one of two main causes — (1) a 

 marked lowering of the land in post-glacial times, with a general climate 

 much the same as that which obtains now ; or (2) a change in the climate 

 affecting a Avide area, or even the earth as a whole. 



Cause of the Change. 



A marked lowering of the land in this region of moisture-laden westerly 

 winds would have the effect of making the climate uniformly humid over 

 the whole of the country, instead of being, as now, subject to an abnormally 

 heavy rainfall on the west of the range, while the east is comparatively dry. 

 With lower mountains the total amount of rain intercepted would in all pro- 

 bability be much less than that which would be intercepted if the moun- 

 tains were higher, but it would be more uniformly distributed. The 

 humidity of the climate depends as much on the number of rainy days 

 as on the number of inches that fall during the course of the year — for 

 example, the cHmate of the Chatham Islands is markedly humid with a 

 comparatively smaU annual rainfall. However, before lowering of the 

 land could produce a humid climate in the Mackenzie country or in 

 Central Otago the land would have to be lowered by hundreds, perhaps 

 thousands, of feet below its present level, in order to allow the extension of 

 the moisture-bearing clouds over the ranges near the coast, so that the 

 interior of the country might receive a share of their moisture ; and there 

 is no evidence of such a lowering since glacial times. Even if the old 

 beaches found in various parts of the south of this Island were post- 

 glacial — which is open to doubt ^ — -the amount of sinking that they 

 indicate is totally insufficient to have produced a moist climate over that 

 part of the country which lies along the east of the range. It seems 

 14* 



