152 The N.Z. Journal of Science and Technology. [May 
All terraces cut by streams have uniform down-valley slopes determined 
by the stream-gradients at the time they formed part of valley-floors. In 
the direction across the valley they are practically horizontal, with the 
exception of some of those developed by lateral swinging, which are lowest 
at the back, where they abut against the concave fronts of the next higher 
terraces. The low strips, now generally swampy, mark the last position of 
the river-channel during a sideward swing, a course from which the river 
was suddenly withdrawn by a cut-off.* Good examples of such swampy 
strips may be seen on the terraces of the Rakaia River previously 
referred to. 
Fig. 13.—Flight of terraces in the Waiau Gorge. 
Flights of Terraces of Composite Origin .—Many groups or flights of 
terraces in New Zealand are undoubtedly of composite origin, resulting 
in part from intermittent uplift, which has certainly taken place, and 
in part from the effects of restrained downcutting. This is the case 
particularly in the valleys of many rivers of the South Island, which are 
broadly opened where they cross the weak rocks of intermont basins, but 
narrow to gorges in crossing hard-rock barriers farther down-stream. The 
investigation of such terrace flights presents most interesting problems, 
most of which, however, must remain insoluble until accurate topographic 
maps are available. 
* W. M. Davis, Geographical Essays, Boston, 1909, p. 519. 
