Morgan. — Geology of the Patea District. 63 



The observations made by Thomson (7, pp. 415-16) and by the present 

 writer support the view that the ironsand of the dunes is mainly derived 

 from the Hawera series. The rich ironsand deposit found on the beach 

 between tide-marks west of the mouth of the Patea River may also be 

 ascribed mainly to material derived from the Hawera series — that is, for 

 the most part it represents a concentration of the material that falls or is 

 blown over the cliffs. 



Probably owing to bhe construction of moles at the mouth of the 

 Patea River, material is at present accumulating on the beach immediately 

 to the west of that river. Consequently cliff-erosion by the sea in this 

 locality has ceased, and a narrow strip of sandhills, perhaps half a mile 

 long, has formed close to the base of the cliffs, as illustrated by the annexed 

 section. 



Geological History — General Remarks. 



The geological history of the coastal belt extending from Wanganui 

 to Hawera has been described by Thomson in his paper on the Hawera 

 series, and some of his statements are almost necessarily repeated in the 

 following paragraphs. At the end of the Castleclifnan stage (Upper 

 Pliocene) the whole of the Wanganui coastal plain (sensu lata) was 

 elevated, not uniformly, but with gentle flexures which, on the whole, 

 produced dips towards the southward. At Wanganui the uplift was 

 not great, perhaps only 400 ft. to 500 ft.; but if Marshall and Murdoch's 

 data (10, pp. 118—19, 127) be accepted it must have been nearly 2,500 ft. 

 at Nukumaru, and not far short of 4,000 ft. at Waipipi. At Patea and 

 Hawera the elevation was not less than at Waipipi, and inland, as a rule, 

 must have been much greater. Owing to the soft nature of the Wanganuian 

 rocks, erosion proceeded rapidly, and when elevation ceased the land was 

 no doubt maturely dissected. Slow depression followed, and the sea, as 

 it advanced over the land, eroded and swept away all material above its 

 own level, thus forming a plane of marine denudation. The great amount 

 of previous erosion and the softness of the rocks enabled it to accomplish 

 this task without difficulty. The plane of denudation, it is fairly obvious, 

 was not horizontal, but had a gentle seaward slope. Inland from Hawera, 

 as previously stated, it is terraced, but in most localities it has the one 

 uniform slope to the foot of the inland hills. Depression ceased when the 

 land was roughly 600 ft. below its present level, and elevation began, 

 apparently almost without delay. During the retreat of the sea the sedi- 

 ments deposited during the previous advance, or the greater part of them, 

 were reassorted, and in great measure swept away. The residue, with 

 new material brought down by the rivers of that time, forms the Hawera 

 series. It is a remarkable fact, perhaps more consistent with Thomson's 

 explanation of their origin than with the writer's, that the Hawera beds 

 seem to have been deposited almost uniformly over the whole of the 

 coastal belt from Hawera to Turakina. Towards Marton they disappear, 

 and their place is taken by fluviatile gravels ; but the country between 

 Marton and the coast has not yet been examined in order to ascertain 

 whether they continue along the present sea-coast towards the mouth of 

 the Rangitikei River. 



Elevation continued till the land was somewhat higher than at present, 

 for there is evidence of recent slight depression at Patea, Waitotara, and 

 Wanganui (Park and Thomson). At the last-named place the depression 

 may have been considerable. A paper by Henry Hill (5) on artesian 

 wells at Wanganui gives data that to some extent support this view. 



