224 Transactions. 



of marine origin, and of material which closely resembles the loess of the 

 south-eastern portion of the South Island. This plain slopes back to the 

 base of the low downs near Amberlev, where it reaches a height of about 

 150 ft. However, on looking up the coast to the north from the mouth 

 of the Waipara, decided remnants of a shore platform can be seen at an 

 estimated height of 250 ft. above the sea, and fronting the plain there 

 are several small remnants at lower levels marking stationary periods 

 during the prolonged elevation. It is therefore certain that a long stretch 

 of coast-line has experienced the effect of this movement. That the rise 

 is of recent date is very clear from the species of shells found at Motunau, 

 and also from the forms of the stream-valleys that have been esta- 

 blished on the elevated marine shelf. With few exceptions, the streams 

 which run across it have very short courses, and are little more than 

 extended gullie& or washouts. Through the somewhat loose Motunau 

 marls, which form the solid base of the land, they have eroded deep 

 channels, at times over 100 ft. in depth, extremely narrow, and with 

 sides so precipitous that they are absolutely impassable for long distances. 

 The whole plain is dissected by them, and they render communication a 

 matter of difficulty where roads and tracks do not exist. The district 

 furnishes a most remarkable example of the effect of a recent upward 

 land-movement on the gradient and cross-section of the stream-channels. 

 The phenomenon is intensified by the uniform seaward dip at moderate 

 angles of the beds under the plain, and the parallelism of the strike to 

 the coast-line. A similar phenomenon is to be observed near the mouth 

 of the Waipara, but the features are not quite so perfect. 



This plain of marine denudation once extended much further sea- 

 ward, and the small island at Motunau is a remnant of it, its flat top 

 show'ing a marked alignment of its surface with that of the coast-line 

 opposite. How t far this plain extended seawards it is impossible to say at 

 present, but at the mouth of the Waipara the river-terraces appear high 

 above the present level of the water, and are terminated suddenly when 

 they reach the edge of the old marine cliff which marks the edge of the 

 coastal plain. At a former period the river must have extended much 

 further seaward, and flowed on the top of the plain, the terraces with 

 their shorn ends giving positive proof of its higher level and seaward 

 extension at that level. As river erosion was proceeding the sea was 

 eating back the margin of the plain, thus giving the streams a steeper 

 gradient and increasing their erosive power, and the truncated ends of 

 the terraces mark the limit to which the plain was destroyed. When one 

 takes into account their perfect condition he must conclude that either 

 terraces are stable land-forms or that marine erosion on this stretch of 

 coast has been vary rapid and comparatively recent. 



There is also evidence of a more recent land-movement still. Along 

 the base of the old marine cliff, referred to previously as bordering the 

 coastal plain, there is a strip of flat land consisting of shingle-beds, sand- 

 dunes, and swamp, half a mile wide and but slightly raised above the 

 sea. It has, without doubt, been formed of detrital matter brought down 

 by the rivers in the vicinity, such as the Ashley and Waipara, as well as 

 by the small streams which flow directly into the sea, their load of 

 waste being distributed by waves, tides, and currents along the base of 

 the old cliff. These accumulations are several miles in length, and their 

 size suggests that there has been either a remarkable increase in the 

 supply of detritus or that there has been a small recent upward move- 

 ment of the coast. There is no apparent reason why the streams should 

 have been suddenly furnished with an increased load of detritus, although 



