Cotton. — Geomorphology of South-western Wellington. 



219 



. .*>m\ 



o 



g 



J3 



is 



GO 



O 

 o 





Another Alternative Explanation. 



An account of the geological history 

 of the coastal lowland which diverges 

 considerably from that assumed in the ex- 

 planation of the physiography here adopted 

 was given by Adkin,* whose account deals 

 in particular with that part of the lowland 

 adjoining the Ohau Kiver. 



Adkin's classification of various stages in 

 his concept of the history of the lowland as 

 Early Pleistocene, Middle Pleistocene, Later 

 Pleistocene (First, Second, and Third stages), 

 and Recent must be discarded, as he had 

 no means of correlation with deposits of 

 Pleistocene age elsewhere ; and for the 

 present purpose the stages " Early Pleis- 

 tocene ' : to ' Recent " may be renamed 

 stages 1 to 6. 



According to his interpretation, at stage 1 

 the Ohau River built a great fan over hypo- 

 thetical undissected uplifted Pliocene forma- 

 tions with a plane surface, the latter being 

 vaguely ;t inferred from the configuration 

 and character of the superimposed fluviatile 

 deposit." Large parts of the surface of 

 the fan formed at this time are regarded 

 as surviving to the present day, though 

 buried by a marine deposit and re-exposed 

 by erosion in the intermediate historical 

 stages. 



Stage 2 was a period of complete sub- 

 mergence of the lowland beneath the sea. 

 This was followed by a period of still-stand, 

 succeeded by uplift continuing to the 

 present day. During the submergence at 

 stage 2a" raised-beach formation " was 

 deposited, consisting of beach sands spread 

 over the whole area of the lowland partly 

 during the advance of the sea and partly 

 during its retreat. This " raised-beach for- 

 mation" comprises the partially consolidated 

 sands of the older lowland. Adkin states 

 that its present level surface is not the 

 original one, as it has been lowered by 

 erosion. It is not clear, however, to what 

 base-level he ascribes the planation, or at 

 what stage of the history it occurred. Dis- 

 section of the surface by small streams is men- 

 tioned in the description of an illustration. 



* G. L. Adkin, The Post-tertiary Geological 

 History of the Ohau River and of the Adjacent 

 Coastal Plain, Hoiowhenua County. North Island, 

 Trans. N.Z. Inst., vol. 43, pp. 496-520, 1911. 



