HYDROGEAPHY. 45 



with the exception of a submarine mountain peak near Ocean Island, 

 is entirely level. The remainder of the distance, though fairly level 

 in general, is interspersed by a number of reefs and mountain ranges. 

 On approaching the great submarine volcanic range running nearly 

 north and south which forms the islands of the Marianne group, at a 

 point a short distance east of Guam, this plain descends into an abyss, 

 which is the deepest yet discovered in the world, lacking only 66 feet 

 of a depth of 6 statute miles. The temperature at this depth was 

 found to be 36° F. It was necessary to select for the cable a route 

 around the northern limit of this depression, which has been christened 

 the Nero Deep. Its southern limits are not yet known. 



Between Guam and the Philippines the bed of the ocean is less regu- 

 lar than to the eastward. For the first 600 geographical miles the 

 depth varies from 1,400 to 2,700 fathoms. The character of the bot- 

 tom is described as undulating, but without definite ranges of hills or 

 valleys. After this a low mountain range occurs which slopes to the 

 westward down to a plain 3,000 to 3,500 fathoms deep, which reaches 

 to the Philippines and has a bottom of soft mud and ooze. 



A route was also surveyed between Guam and Yokohama, Japan, to 

 the westward of the Mariannes and to the eastward of the Bonin 

 Islands. For the first 500 geographical miles a level plain 2,100 fath- 

 oms deep was found. Then the Nero encountered a submarine moun- 

 tain range which apparently connects that of the Marianne Islands 

 with the range extending from the Bonin Islands to Japan. While 

 crossing this range a submarine conical peak was discovered resem- 

 bling Fujiyama in form. a 



Ocean currents. — The currents in the vicinity of the Marianne 

 Islands are much affected by the prevailing winds. During the 

 greater part of the year there is a drift to the westward or south- 

 westward of 1 to 2 knots per hour. On the sandy beaches of the 

 east coast of the island of Guam driftwood of American origin is often 

 found, including huge logs of Oregon fir. From July to September, 

 when the easterly winds are interrupted by the influence of the south- 

 west monsoon, the drift is frequently to the northeast. 



Tides. — The rise of tides in the archipelago is generally less than 3 

 feet. In the harbor of San Luis de Apra the rise and fall is 3 to 4 

 feet. High water occurs there at the full and change of the moon at 

 about seven hours after its meridian passage. The tides play an 

 important role in the economy of vessels lying in the harbor, as the 

 water on the reef is too shallow to permit boats of considerable size 

 to land cargo at any time but that of high water, and it is not unusual 



a See "Trans-Pacific submarine telegraph cable survey," in the Report of the Sec- 

 retary of the Navy for 1900, pp. 299-302, from which the above information is 

 derived. 



