J. D. Dana — Deep troughs of the Oceanic depression. 193 



In the plotting of oceanic bathymetric lines from the few 

 lines of soundings that have been made, the doubts which con- 

 stantly rise have to be settled largely by a reference to the gen- 

 eral features of the ocean, and here wide differences in judg- 

 ment may exist in the use of the same facts ; but through the 

 depths stated on the map, the reader has the means of judging 

 for himself. In the case of an island the lines about it may 

 often have their courses determined by those of adjoining 

 groups, or by its own trend ; but in very many cases new 

 soundings are needed for a satisfactory conclusion. 



Some divergences on the map from other published bathy- 

 metric maps require a word of explanation. The northern 

 half of the l^orth Pacific is made, on other deep-sea maps, 

 part of a great 3000-fathom area (between 3000 and 4000) 

 stretching from the long and deep trough near Japan far 

 enough eastward to include the soundings of 3000 fathoms and 

 over in mid-ocean along the 35th parallel. It has seemed 

 more reasonable, in view of present knowledge from sound- 

 ings, to confine the deep-sea area off Japan to the border- 

 region of the ocean, near the Kurile and Aleutian islands, and 

 leave the area in mid-ocean to be enlarged as more soundings 

 shall be obtained. Again in the South Pacific, west of Pata- 

 gonia, the area of relatively shallow soundings (under 2000 

 fathoms) extending out from the coast, is on other maps bent 

 southward at its outer western limit so as to include the area 

 of similar soundings on the parallel of 40° and 50°, between 

 112° and 122° W. The prevailing trends of the ocean are op- 

 posed to such a bend, and more soundings are thought to be 

 necessary before adopting it. 



It may be added here that in the Antartic Atlantic, about 

 the parallel of 66|° S. and the meridian of 13^° W., a large 

 area of 3000 and 4000 fathoms has been located. It was based, 

 as I have learned from the Hydrographic Department of the 

 British Admiralty, on a sounding in 1842 by Capt. Ross, R. 

 ~N., in which the lead ran out 4000 fathoms without finding 

 bottom. The sounding was, therefore, made before the means 



published is necessarily small, and none of the ordinary maps of the oceans give 

 either deep-sea soundings or a correct idea of the trends of the oceanic ranges 

 of islands, I state here- that the charts of the U. S. Hydrographic Department 

 for the Atlantic, Pacific, Indian and Arctic oceans may be purchased of dealers 

 in charts in the larger sea-hoard cities for 50 cents a sheet and less according to 

 size. (There are several large charts to each ocean). One of the firms selling 

 them in New York City is that of T. S. & J. D. Negus, 140 Water st. The 

 British Admiralty have published a map of the Pacific with its soundings on a 

 single sheet, and for the Atlantic and Indian oceans with part of the Pacific, be- 

 sides charts of the Antarctic and Arctic seas. The occasional bulletins from the 

 Hydrographic Department and Petermann's Mittheilungen contain nearly all the 

 new data issued for the perfecting of such a chart. 



