REPORT ON OCEANOGRAPHY 79 



Echo sounding profiles across the New Zealand continental shelf 

 are being accumulated for study. Many profiles show the shelf to be 

 terraced. The resurvey of Cook Strait by H.M.N.Z.S. Lachlan has 

 shown that a submarine canyon drains southward from the relatively 

 shallow (50-fathom) shelf of the western strait to depths in excess of 

 1,100 fathoms south of Cape Palliser. Shallow tributary channels cross- 

 ing the shelf between Nelson and Taranaki bear no relation to the 

 mouths of rivers. The resurvey has shown changes in the walls of the 

 Cook Strait Canyon since the early surveys of last century. 



During 1950, D. J. Banwell and B. H. Olson measured electric 

 potential differences between points on shore spaced 2-3 kilometres 

 apart, considered due to tidal currents (Couper, 1953, Rep. 7th N.Z. 

 Sci. Congr. 3). Previous measurements (e.g. by Barber) were made in 

 the northern hemisphere. The results agreed fairly well with the theo- 

 retical argument of Longuet-Higgins, given the opposite polarity of 

 the earth's field. 

 New Zealand Geological Survey T ' 



Echo sounding and other bathymetric records were filed at the Geo- 

 logical Survey from 1949 until 1952 when the Geophysics Division un- 

 dertook their custody. 



The topography and sediment of Mernoo Bank, an oval elevation 

 of the sea bottom rising from depths greater than 200 fathoms to 28 

 fathoms, 90 miles east of Canterbury, were described by Fleming and 

 Reed (1951, N.Z. J. Sci. Tech. B 32 (6): 18-30) on the basis of an echo 

 sounding survey by H.M.N.Z.S. Lachlan, and serial magnetometer profile 

 and sediment samples. The bank is interpreted as a tectonic dome, 

 composed of late Paleozoic to early Mesozoic indurated sediment, sculp- 

 tured by shallow radial submarine valleys. J. J. Reed has studied the 

 grain-size, sorting, and mineralogy of sediments of the Sumner estuary, 

 Canterbury (1951, N.Z. J. Sci. Tech. B 33 (2): 129-37). From the Cha- 

 tham Rise west of the Chatham Islands, R.R.S. Discovery II dredged 

 coarse sediment at a depth of 170 fathoms containing pebbles of schist 

 and of phosphatised Miocene globigerine limestone (Reed and Horni- 

 brook, 1952, N.Z. J. Sci. Tech. B 34 (3): 173-88). Reed has prepared a 

 sediment map of Cook Strait based on mechanical analysis of 170 sam- 

 ples, mostly collected with a Worzel sampler from H.M.N.Z.S. Lachlan. 

 Few samples had been obtained from the floor of the Cook Strait Can- 

 yon, but the general pattern indicates that sediment is coarse near the 

 canyon and fine on flat shelf areas distant from it. Calcite and siderite 

 concretions, some of them fossiliferous, a foot or two in diameter, are 

 regularly caught on fishing lines on the sides of the canyon and have 

 been studied by C. A. Fleming. The concretions contain fossils pro- 



