Cotton. — The Uplifted East Coast of Marlborough. 289 



area. McKay* notes the presence of Awatere River gravels on low hills in 

 this vicinity. This ancient surface, now dissected, but indicated by an 

 even sky-line (see fig. 3), slopes gently seaward, and apparently two trigo- 

 nometrical stations, at heights of 352 ft. and 355 ft., close to the edge of 

 the cliffs bordering Cook Strait, are situated on it. Some flat-topped 

 remnants near the south-east bank of the Awatere River, at a distance of 

 about three miles from the sea, reach a height of 543 ft., but the writer 

 failed to note whether they are accordant with the last-mentioned surface 

 or stand above it. 



During a later — the last — long pause in the general movement of uplift 

 fairly broad valley-floors were cut by the Awatere and neighbouring smaller 

 rivers upon the weak rocks. In the vicinity of the railway bridge the broad 

 terrace plains on either side of the Awatere River, remnants of the flood- 

 plains of this period, together have a width of three miles, and are at a 

 height of 290 ft. above sea-level and 120 ft. above the present level of the 

 river. 



The river now wanders in braided channels on the gravel-covered floor 

 of a trench a few hundred yards in width. Such braided courses are now a 

 common feature of New Zealand rivers, and, of course, indicate excess of 

 waste supply over transporting-power, resulting in aggradation. In the 

 writer's opinion, the present excess of waste in Marlborough is largely, if 

 not wholly, the results of destruction of the original vegetable covering of 

 the land as a result of settlement. The excessive supply of waste more 

 than balances the effect of a very recent, small movement of uplift in Marl- 

 borough, which will b? mentioned later, and which, other things being equal, 

 would have resulted in degradation. The writer has been informed by 

 E. A. Weld, Esq., of Flaxbourne, that the bed of the Flaxbourne River has 

 been perceptibly raised, and it is said of the Kekerangu River, which now 

 flows in braided channels on a broad gravel bed, that in the early days of 

 settlement it was a " swamp stream " — that is, had a marshy flood-plain. 

 Speight regards the cause of similar aggradation in Canterbury rivers as 

 climatic. f • 



With respect to present sea-level as base-level the lower course of the 

 Awatere is graded, but its declivity is still steep, being something like 25 ft. 

 or 30 ft. per mile. The vertical concave banks and the convex banks 

 descending gradually as series of terraces indicate that the curves of the 

 stream have been enlarged contemporaneously with down-cutting. Con- 

 sidered in connection with the extreme weakness of the rocks in which 

 the river is working, the youth of the present valley indicates that the 

 latest important uplift — that is, the one that interrupted the last long 

 plain-cutting pause — -took place very recently. Tributary streams flow for 

 long distances over the surface of the uplifted flood-plain, and rejuvenation 

 has reached but an insignificant distance from their mouths. An example 

 of these is Starborough Creek, { which enters the Awatere on the south-east 

 side, a short distance below th^ railway bridge. 



In the neighbourhood of Flaxbourne (or Ward) there is similar proof 

 of pauses in the general movement of uplift, the pauses being sufficiently 

 long there also to allow of the excavation of extensive valley lowlands by 

 the local streams where these flowed over the weak Awatere beds. In 

 places the intervening ridges were cut right through, continuous lowlands 



* A. McKay, Geol. Surv. of N.Z., Rep. Geol. Expl. during 1885 (1886), p. 125. 

 t See footnote to p. 294. 



I This tributary, flow ng for about five miles over the surface of the uplifted flood- 

 plain, parallel with the main stream, affords an example of a "postponed junction." 



10- Trail *. 



