C'OTTOX. — Block Mountains and a " Fos-nl " Denudation Plain. 



59 



Art. YI. — Block Mountains and a " Fossil " Denudation Plain in 



Northern Nelson. 



By C. A. Cotton, D.Sc, F.G.S., Victoria University College, Wellington. 

 [Read before the Wellington Philosophical Society, 27th October, 1915.] 



Plates IV, V. 



Contents. 



Introduction 



_" Block "" features throughout New Zealand 



Northern Nelson 



The Aorere-Gouland depression 



The Wakamarama fault -scarp 



The north-eastern portion of the scarp . 



Tilted and stripped plateau of the south 



Erosional, sedimentary, and deformational history 



Dissection . . 



The actual valley of the Lower Aorere 

 The Gouland Downs depression 



The floor . . 



The eastern boundary 



A " catenary " saddle 



The Slate Range 



The drainage and dissection of the Gouland Downs 



eastern side of the Aorere Valley 



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Introduction. 



For some years the writer has been interested in the geomorphogeny of 

 northern Nelson, and in 1913, though at that time without personal 

 knowledge of the district, he presented a brief note on the subject before 

 the Geological Section of the Wellington Philosophical Society, question- 

 ing in some measure the interpretation of the relief given by Bell in 

 the Parapara bulletin of the Geological Survey.* The views then ex- 

 pressed having been favourably received by geologists acquainted with 

 the district, and Professor W. M. Davis having in the meantime advised 

 him to take up the subject of block mountains in New Zealand, the 

 writer paid two visits to northern Nelson in 1915, and is now able to 

 give a detailed description of a small portion of the district, and to 

 express some general opinions as to the remainder. In this paper a 

 condensed and generalized description of northern Nelson is given, and 

 that is followed by a more detailed description of some features of the 

 Aoi'ere Valley and of the Gouland Downs. 



" Block " Features throughout New Zealand. 



As a result of observations made in many parts of New Zealand at 

 various times, and confirmed by special visits recently made to a number 

 of critical localities, the writer has come to the conclusion that the 

 present relief is very largely— almost entirely — due to recent differential 

 movement of crust blocks, both large and small. Though this explana- 

 tion of the relief is not to be found in any general work on the geology 



* J. M. Bell, " The Geology of the Parapara Subdivision," N.Z. Geol. Surv., Bull. .3, 



1907. 



