Dr. TuUy remarked that the steep walls and flat floors of the land 

 canyons can be followed out to sea, and then asked if Dr. Shepard had 

 investigated the canyon off the boundary of Canada and U.S.A., which 

 was 2,000 fathoms at the inner limits and 2,000 to 3,000 fathoms at the 

 outer limits. 



Dr. Shepard considered the upper part of this canyon to be a glacial 

 trough, but out beyond that it was a typical submarine canyon. 



Dr. Tully asked how the steepness of the canyon wafls could be main- 

 tained, and Dr. Shepard replied that all the troughs have extremely 

 steep walls, and may be a result of the constant disintegration resulting 

 from marine borings. The glacial valleys have steep walls, but all types 

 of barred basins that the canyons have not. You would maintain then 

 that these canyons are fundamentally of the river origin, said Dr. Tully, 

 and in reply Dr. Shepard agreed, stating that they are at right angles to 

 the coast, whereas fault-structures are parallel to the coast. Dr. Shepard 

 then exhibited the depth-sounding records of the steamer express from 

 Wellington to Lyttelton. 



Dr. Cotton said that the submarine canyons were quite obvious 

 features of submergence, but could not local movements of land produce 

 the submergence ? On the New Zealand Marlborough coast enormous 

 block-faults are a prominent feature, and there may be block faulting 

 under the sea off the coast. He felt he could not trust subjective 

 contouring of the large canyons as much as that of the smaller canyons. 



Dr. Shepard agreed that the subjective drawing of the contours by 

 Veatch and Smith must be treated with reserve. 



Mr. Fyfe remarked that several years ago the Union Steamship Co. 

 .carried out extensive traverses taking depth soundings from Cape 

 Campbell to Akaroa. The contours indicated that the canyons in this 

 area mentioned by Dr. Shepard were basin-shaped and parallel to the 

 coast, and he agreed with Dr. Cotton that they were probably structural. 

 Dr. Cotton added that if such canyons are found off the Dunedin coast he 

 would not question them because the geology at Dunedin is different 

 from that at Kaikoura. 



Mr. Healy asked if these might not have been warping apparently 

 round the margin of the Pacific which is an active belt, but, on the other 

 hand, Dr. Shepard had illustrated similar canyons in the stable areas of 

 the Atlantic. Did the longitudinal profile show warping or not ? 



Dr. Shepard replied that under- water canyons are just as large on 

 the Atlantic coast as they are on the Pacific" and that the longitudinal 

 profiles did not show any warping. He was inclined to agree with 

 Dr. Atwood in stating that they were cut very rapidly. 



In reply to Dr. Westerveld's query — Do these canyons go to different 

 depths or are they fairly constant ? — Dr. Shepard said, " That is our 

 weakest point and will be the subject of further investigation with the 

 improved apparatus that is now being installed." He could not say 

 definitely that they all ended at a certain more or less constant depth. 



NOTE ON DROWNED ISLANDS IN THE PACIFIC 



By Richard A. Sonder, Zurich, Switzerland 



It seems of interest in the framework of this symposium to call attention 

 to a curious level problem connected with the flat-topped seamounts 

 existing in great number in the Pacific. As I have presented a more 

 extensive paper to the eighteenth International Geological Congress 

 in London, only a short exposition will be given hereafter. 



332 



