282 The N.Z. Journal of Science and Technology. [Sept. 
lithosphere, or “ crust,” is not rigid, but yields under a load ; and so the 
folded rocks may sink until isostatic equilibrium is restored, a place being 
made for them by lateral flow of deeply buried rocks. As to the cause 
of the broad upswellings of the surface that have taken place later and 
have led to deep dissection and the sculpture of mountains nothing is 
known. 
Block Mountains. 
Instead of even uplift .or broad doming taking place to form a plateau 
that is later destroyed by erosion, the land surface is sometimes broken 
into blocks some of which are uplifted, either evenly or irregularly, while 
others either sink or remain stationary. The surface that is thus broken 
may previously have strong relief, low relief, or no relief at all: it may 
be part of a sea-floor. The underlying rocks may or may not have a 
folded or otherwise deformed structure. 
The uplifted blocks and the higher parts of tilted blocks form initial 
mountains, or mountain-ranges, upon which erosion begins at once its 
work of dissection and sculpture. Block mountains thus formed are strictly 
one-cycle mountains, and yet, when the surface of the initial form is an 
eroded surface, perhaps truncating deformed structures, they are seen to 
be closely akin to the multi-cycle mountains described above, differing 
from them in that the uplift to which they are due is differential instead 
of regional. 
In various parts of the world block mountains are known in which 
sculpture is not so far advanced but that the initial form is still clearly 
traceable. On the summit of a block (or on the back slope of a tilted 
block) this is generally an earlier land surface, while along the lines of 
fracture between adjacent blocks there are fault-scarps. 
i 
The Mountains of New Zealand.* 
Formerly the mountains of New Zealand—that is to say, the Southern 
Alps and other chains formed of the older rocks—were regarded as one- 
cycle fold mountains, though the great length of the period that has 
elapsed since the folding is sufficient in itself to render this explanation 
extremely doubtful. In recent years the opinion has been gaining ground 
that the original fold mountains were more or less completely destroyed 
by erosion prior to an uplift which initiated the sculpture of the present 
ranges. The writer has now put forward the view that not only were the 
fold mountains destroyed by erosion, but also that their site was largely 
covered by younger rocks, and that the later uplifts, to which the present 
relief is due, were differential. To these the name “ Kaikoura orogenic 
movements ” is applied. The features to which they gave rise are still, 
in some parts of New Zealand, well-preserved block mountains, and practi¬ 
cally everywhere the tectonic nature of the relief is still recognizable. 
New Zealand may, in fact, be described as a concourse of earth-blocks, the 
highest of which lie on the north-east and south-west axis of the land- 
mass. 
The initial surfaces of the blocks- over a large part of the region were 
portions not of a previously eroded land surface, but of a plain of deposition, 
* C. A. Cotton, The Structure and Later Geological History of New Zealand, 
Geological Magazine, dec. 6, vol. 3, pp. 243-49, 314-20, map, illus., 1916 ; Block 
Mountains in New Zealand, American Journal o/ Science, ser. 4, vol. 44, pp. 249-93, map, 
diagrs., illus., 1917. 
