Adkin. — Poxt-teriiarij Geological l/ixfori/ of Oluni Fiver. 513 



In this inaniier the Horowheiiua Lake was formed. The waters of 

 tne river gradually banked up behind the sandy barrier, finally filling the 

 wide channel as far up as the present site of Levin. At the time of its 

 maximum extension the Horowhenua Lake must have had an area of be- 

 tween five and six square miles, its former eastern and south-eastern margins 

 being indicated by the presence of a black soil on the surface of the shingle 

 of the Ohau fan. The uppermost edge of the area of black soil ex- 

 tends from Levin to AVeraroa, and from thence along the Beach Road 

 to the State farm, and is, of course, a relic of the swamps which fringed 

 the former successive margins of the lake. During its maximum exten.sion 

 the greatest depth of the lake was about 100 ft., the level of its Avaters 

 being for a while kept fairly constant by an overflow between the sand- 

 hills to the sea. When, however, by the enlargement of this outlet the 

 Hokio Stream came into existence, the surface of the lake was more or 

 less gradually lowered mitil it reached its present level, thereby reducing 

 its area by three-fourths, and diminishing its deptb by more than 70 ft. 

 The irregular swamps at the north and south ends of the lake are the 

 relics of arms of that sheet of water when it had attained its greatest 

 extent, or are abortive attempts to gain an outlet to the sea, or perhaps 

 both. 



Former levels of the Horowhenua Lake are indicated by the position 

 and elevation of the extremities of the alluvial deposits of streams which 

 at one time flowed into it. The previously mentioned " Kimberley Road " 

 stream flow^ed into the southern end of the lake when its level was rising. 

 The Koputaroa has also left memorials of the former higher levels of the 

 lake. The first branch of its western outflow reached the lake when the 

 surface of the latter had attained its maximum altitude — about 110 ft. 

 above the present sea-level ; while the second branch entered the lake 

 when its surface had been lowered to about 70 ft. above that datum-line. 



At the present time the Horowhenua Lake has an area of 900 acres, 

 its surface is 36 ft. above sea-level, and its greatest depth probably does 

 not exceed 30 ft. The lake derives its water-supply from the overflow 

 of the adjacent swamps and from their interfluent streams, and its only 

 outlet is the Hokio Stream, the sluggish waterway which meanders between 

 the sandhills to the sea. The six islands situated near the western and 

 southern shores were artificially constructed by the Maoris in the early part 

 of the last century to serve as fortresses in their intertribal wars. Some 

 are now, however, more or less submerged through the wasting-away of 

 the perishable vegetable matter of which they were partly constructed. 



The sandhills which enclose the Horowhenua Lake on its western and 

 southern shores have kept pace with the uplift of the land, so that they 

 now cover the strip of country, three miles ■v\ade, which borders the sea. 

 On the southern boundary of the county the belt of sandhills is also three 

 miles in width, but at its northern end the blown sand has spread inland 

 for over six miles. The most advanced inroad of blown sand is situated 

 near the northern end of Lake Horowhenua, where a comparatively thin 

 stratum extends from the main belt of dunes to the Heatherlea cross-roads. 

 This tongue of land has long ceased to drift, but it can be distinguished 

 from the underlying raised-beach sandstone by its finer texture, its less 

 regular structure, the absence of parallel laminae, and its hummocky upper 

 surface. The superimposition of the blov/n sand upon the raised-beach 

 sandstone can also be seen about one mile south of Lake Horowhenua. 



17— Trans. 



