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thousand acres in extent, most of it permanently under water, and separated 

 from the sea by a narrow boulder-bank 8 ft. to 16 ft. above sea-level. All 

 the material in this boulder-bank is from the Awatere River, and includes 

 large quantities of the volcanic rocks brought down by the tributaries from 

 the dvkes in the Kaikoura Mountains described by McKay, and more 

 recently by Thomson.* The Wairau River, indeed, has not yet carried 

 any gravel to the sea, the limit to which it has so far carried any being just 

 below the railway bridge, which is several miles from the shore-line. 



The rivers that cross the plain afford further evidence as to the manner 

 of its formation. The largest, the Wairau, meanders over a wide stretch 

 of country, and provides two very fine examples of an ox-bow curve and 

 one of an ox-bow cut-off. The first curve occurs a little below the point 

 where the Blenheim-Picton Railway line crosses the river, the cut-off is 

 about a mile and a half lower down the river, and the other curve is 



sketch map „f 



THE WAIRAU PLAIN, 

 MARLBOROUGH. 



WHITE 

 BLUFFS 



about a mile and a half lower down again. The next-largest river, and 

 the most important, in that it makes the Town of Blenheim accessible to 

 small steamers, is the Opawa. This is a distributary of the Wairau, and 

 the two enclose, the greater part of the delta formed when the Wairau 

 entered the still waters of the lagoon. The Opawa is a perfect example of 

 a meandering river. The shortest course possible to it from Blenheim to 

 the point where it rejoins the Wairau near the sea is four miles and a half 

 long ; the actual course taken by the river in its windings between these 

 two points is over nine miles and a half in length. 



These and other facts contribute to an understanding of the geological 

 history of the area. The whole plain is a flat surface slightly tilted towards 



* Trans., N.Z. Inst,, vol. 45, 1913, p. 308. 



