312 Transactions. 



(5.) Fluviatile Hanging Valleys. 



Hanging valleys having the typical V-shaped cross-section of stream 

 erosion, and which owe their present state as such to the former presence 

 of a glacier, are found in Park Valley only. The best examples are situated 

 on the left wall of the valley, about three-quarters of a mile below the 

 main cirque. The height of the falls which descend from their lower 

 ends into the main valley is now greatly reduced by the infilling of the 

 latter with scree-material. In the glaciated part of Park Valley the fluvia- 

 tile hanging valleys are the sole remaining relics of its pre-glacial form — 

 a form due entirely to fluviatile erosion. Prior to the glacial period the 

 portion of Park Valley referred to was very much narrower, and also rather 

 less deeply excavated than it is at the present time. From the ridges 

 forming the watersheds on either side of the valley steep lateral spurs ran 

 down to the valley-bottom, and the intervening gullies were in topographic 

 adjustment with the trunk valley. 



With the advent of the ice the pre-glacial topography of the upper 

 portion of Park Valley was modified in two ways — the valley was both 

 deepened and widened. The deepening was relatively greater in some 

 parts of the valley than in others ; in the main cirque the valley was over- 

 deepened and the gradient of its floor reversed. Throughout the glaciated 

 part of the valley the deepening was sufficient to remove all traces of the 

 V-shaped contour of the pre-glacial trench, and to give the valley the 

 typical flat bottom of glacier erosion. The widening of Park Valley by 

 ice-action was of even greater extent and importance. In the achievement 

 of this result the lateral spurs were deeply truncated, the intervening 

 gullies betrunked and converted into hanging valleys, and the sides of the 

 main valley cut back to such an extent as to give them a steep wall-like 

 character. The present fluviatile hanging valleys were never ice-filled, 

 but at the time of maximum refrigeration the tributary gullies nearer the 

 head of the main valley were filled with ice, and were moulded thereby 

 into their present U-shaped form. These TJ-shaped hanging valleys owe 

 their present state as such more to the rapid erosion of the main cirque 

 by the process known as " plucking " than to the lateral grinding which 

 produced the fluviatile hanging valleys. 



The Topography of Park Valley. 



(See map, p. 311, and Plates XX1I-XX1V.) 



The topography of the upper portion of Park Valley is undoubtedly 

 of glacial origin. The valley contains the most extensive and the best- 

 preserved memorials of the erosion of glacier-ice, and therefore it has the 

 distinction of being the former site of the largest of the extinct glaciers 

 of the Tararua Ranges. The general trend of the glaciated part of the 

 valley is west by south, but it is not straight ; it runs in two curves — the 

 upper bending southward, the lower northward. From the lower limits 

 of glacial erosion the valley turns south-south-west and south-east to its 

 junction with the Waiohine-iti River. This part of Park Valley is narrow 

 and gorged. Lofty ridges form the boundaries of Park Valley, and the 

 highest points of these — Mounts Thompson, Lancaster, and Dora, and 

 Arete Peak — encircle its head, and in the past formed the gathering-ground 

 oi the perennial snowfields which fed the old glacier. 



