108 



Transactions. 



Art. XV. — Further Notes on the Horowhenua Coastal Plain and the 



Associated Physiographic Features. 



By G. Leslie Adkin. 



[Read before, the Wellingfon Philosophical Society, 18th SejJtember, 1918 ; received by 

 Editor, 18th September, 1918 ; issued separately, ::6th May, 1919.] 



In this paper I present further data bearing on the history of the Horo- 

 whenua coastal plain and the associated Quaternary deposits, and also 

 discuss some of the main points raised by the dissension of opinion between 

 Dr. Cotton* and myself. f 



Dimensions and Eastern Limits of the Horowhenua Coastal Plain. 



As shown by the following table, the Horowhenua coastal plain attained 

 its maximum breadth of twenty-six miles in the vicinity of Palmerston 

 North, J and gradually narrowed in a south-westerly direction. 



The thickness of the coastal-i^lain formation|| depends upon the relief of 

 the early Pleistocene laud-surface upon which it lies, attaining its maxima 

 and minima along the margin of the old land according to its remoteness 

 from or proximity to the apexes of the Ohau, Otaki, and other fans. Two 

 miles south of Shannon the formation lies on the lower part of the northern 

 slope of the Ohau fan, and there its original thickness was about 500 ft. 

 On the lower edge of the southern slope of the fan of the Manawatu River, 

 near the margin of 1he old land due east of where Linton now stands, its 

 former thickness probably exceeded 600 ft. These figures are only approxi- 

 mate, and require to be verified or corrected by calculations based on 

 careful surveys. 



* C. A. Cotton, The Geomorphology of the Coastal District of South-western 

 WelUngton, Traiis. N.Z. Inst., vol. 50, pp. 212-22, 1918. 



t G. L. Adkin, The Post-Tertiary Geological History of the Ohau River and of 

 the Adjacent Coastal Plain, Horowhenua County, North Island, Trans. N.Z. Inst., 

 vol. 43. pp. 496-520, 1911. 



% The writer has at present no data as to the extent of the Horowhenua coastal 

 plain north of this point, beyond which, however, it is known to extend. 



§ These are the altitudes of the highest traceable sandstone in the localities specified. 



II The term " raiscd-beach formation " has been abandoned as being misleading, 

 substituting " coastal-plain formation," " coastal-plain sandstone," or, more briefly, 

 " sandstone formation." 



