180 General Remarks on the High Mountain Vegetation. 
Topographical changes are of course of prime importance both with regard 
to the evolution of vegetation and species. At the present time, the great 
prevalence of mountains composed of greywacke and allied rocks which supply 
debris in enormous quantity leads to the constant establishment of migratory 
formations both progressive and retrogressive. Although such formations are 
from their nature transient, yet they are constantly being re-established, so 
that they present permanent habitats where habitat-effects can accumulate and 
new species arise. Disintegration of the surface-soil, the result of wind, snow, 
frost and rain action, is always in progress, especially where steppe-conditions 
prevail, so that the surface is not even like a meadow but there are low 
raised mounds of vegetation surrounded by sunken bare patches. Many other 
details as to habitat-ecology are cited when dealing with the formations. 
a a N hapter I en \ 
iR The leading Physiognomie Plants and their Growth-forms. 
New Zealand, 
in number, | 
