222 Transactions. 



which have a combined area of about forty square miles. Some parts 

 of their surfaces are thickly covered with small boulders or coarse gravel ; 

 others have a gravelly soil ; while others, again, have a superficial layer of 

 silt overlying gravel. Most of the fans are trenched and terraced to a small 

 extent. The surfaces of the fans and of terraces cut in them are very 

 similar to one another, as are also gravel-covered terraces within the border 

 of the old land. All these may be classed as gravel plains. The gravel- 

 bearing streams are at present aggrading as though to refill the trenches 

 in the fans. The actual stream-beds are,' therefore, areas of bare gravel 

 over which the streams flow in changing, braided channels. As previously 

 mentioned, the upper surface of the Otaki formation passes in some places 

 into that of a fan without any abrupt break of slope. 



The Delta of the Manawatu. 



More or less analogous with the fans of the. southern part of the lowland 

 is the delta of the Manawatu River ; but this is one, perhaps the chief, of 

 the sand-supplying rivers. Its delta is composed mainly of fine material, 

 and its gradient is very gentle as compared with that of the gravel fans. 

 The Manawatu delta forms a plain of wide extent lying at present almost 

 entirely on the north side of the river, and continued up-stream by a wide 

 flood-plain, below which the river is now slightly entrenched, and above 

 which there are broad terraces on the northern side. The seaward margin 

 of the delta is covered with dunes, some belts of which extend inland many 

 miles. The Manawatu River at present bends to the south-west after 

 emerging from its gorge across the old land, and at a not very distant date 

 it swung still farther to the south. The toe of the bench formed by the 

 Otaki series is here cut back to a line of cliffs by the action of the river, 

 and at the base of these a considerable area of ill-drained flood-plain, now 

 abandoned by the river owing to its slight entrenchment, forms the great 

 Makurerua Swamp (see fig. 1). The whole of the delta plain was formerly 

 swampy, but a great part has been artificially drained. 



The Modern Dunes. 

 The modern dunes are built of grey sand similar to that forming the 

 sandstone of the Otaki series. All except a narrow belt close to the sea 

 are fixed by vegetation, but beneath the superficial layer of humus the 

 sand is still quite loose. The belt of dunes has a width of from three 

 to six miles, and their average height is 170 ft. Adkin notes that 

 their general arrangement is in ridges at right angles to the coast-line.* 

 The shore-line of the dune-covered foreland advances as a broad cusp 

 towards Kapiti Island (a high island of old rocks some four miles from the 

 mainland). This is evidently an early stage of island-tying. 



Lakes and Swamps. 

 Several lakes and many small ponds and swamps formed by the silting- 

 up of ponds lie between the modern dunes and the margin of the other 

 physiographic elements of the lowland, and there are many swampy areas 

 among the modern dunes. The valley-floors in the Otaki formation are 

 practically all swampy, as a result either of normal aggradation with fine 

 silt or of ponding by sand-dunes followed by accumulation of silt. The 

 largest swamp in the district — the Makurerua Swamp — has been referred to 

 above. 



* G. L. Adkin, loc. cit., pp. 514-15. 



