151 
1918.] The N.Z. Journal of Science and Technology. 
Beautiful examples of rock-defended terraces occur in the valley of 
the Bakaia River, at the Rakaia Gorge.* The terraces are composed of 
alluvial gravel, through which the 
river has cut slowly downward, and 
the defending ledge is a bar of 
igneous rock crossing the course of 
the river. 
Terraces formed in the manner 
just described will not occur at the 
same height on opposite sides of a 
valley, but if present on both sides 
will alternate as in fig. 11 , A ; for, 
obviously, the meander belt takes 
a considerable time to migrate 
from one side of the valley to the 
other, and by the time it has 
crossed it has reached a lower level. 
Neither is there necessarily a symmetrical development of terraces on both 
sides : in parts of the valley terraces may be entirely absent on one side 
or the other. In those terraces, on the other hand, which mark the 
Fig. 11.— -Diagrams of terrace profiles. 
* See R. Speight, Some Aspects of the Terrace-development in the Valleys of the 
Canterbury Rivers, Trans. N.Z. Inst., vol. 40, pp. 16-42, 1908. 
[/?. Speight , photo. 
Fig. 12. —Flight of terraces in the Broken River Basin. 
development of flood-plains in brief cycles separated by episodes of uplift 
there will be perfect accordance of height where terraces are present on 
both sides, and at some points there may even be perfect symmetry in 
the width of terraces. 
