The largest gulf on the north-west coast, off Puget sound and British Columbia, even at a great distance from land, reaches only the relatively small depth of less than 3,00o metres. East of 150° W. the Pacific has few islands; the oceanic islands are volcanic, and coral formations are, of course, scanty. The most important group is the Galapagos islands. On the other hand in the western Pacific we have numberless great and small islands and island groups. They are sometimes set out in regular chains, at other times spread out irregularly over great areas. To the first type, in the north, belong the Aleutians, the Kuriles, the Japanese islands, the Riu-Kiu islands, the Philippines, and parallel to them the Pelew islands, the Yap group, the Bonin and Mari anne group; in the Southern Hemisphere, the Solomon islands, the New Hebrides, New Caledonia and New Zealand. New Zea land morphologically is related northward to the Kermadec and Tonga islands, and southward through the Auckland islands to Macquarie island (55o° S.). On the outside of nearly all these island chains are oldserved very deep, and sometimes fairly wide, trenches, in which depths of over 8,000, even over io,000 metres, have been registered. This is the most important characteristic of the configuration of the Pacific floor; no other ocean has any thing like it. The greatest deeps are the Aleutian trench (7,382 metres), the Kurile-Japanese trench (8,514 metres), the Philip pine trench, eastward of north Mindanao in lat. 9° 42' N.
and long. 126° 51' E., only 75 km. from the coast where in 1927 the German cruiser "Emden" measured the greatest of all sea depths, viz., 10,80o metres. In the same latitudes three other trenches are known, east of the Palau islands, east of Yap and south-east of Guam and the Marianne islands, where the United States telegraph ship "Nero" found a depth of 9,685 metres.
In the Southern Hemisphere between New Guinea and the Solomon islands is the Bougainville trench (9,14o metres). The New Caledonian trench has a depth of 7,57o metres. Finally, H.M.S. "Penguin" explored the Kermadec-Tonga trench which lies outside; i.e., eastward of these groups between 36° S. and 16° S. and includes depths attaining 9,412 metres. The area of these long, deep regions is always small; these deeps lie parallel to the coasts of the present continents or to the coasts of earlier continents. In earlier geological epochs, for example, a continent may have extended eastward from New Guinea to the Tonga islands and New Zealand, and perhaps north to the Mariannes. It is certain that in these trenches, which lie in front of the fold mountains of eastern Asia, is to be sought a centre of great tec tonic disturbances; just as the west coast of South America is afflicted by terrible earthquakes, whose epicentre lies in the trenches off Chile and Peru. The immense stretches of the west Pacific contain, besides these regular island groups and deeps, many irregularly strewn islands ; e.g., the Hawaii islands, the Carolines, the Gilbert islands, the Samoa archipelago, the Tau motu archipelago, etc. Most have volcanic cores; in low lati tudes these islands are surrounded with coral reefs, or it may be that the reefs alone appear as atolls. In the great areas be tween these groups the sea floor sinks to depths exceeding 4,000 metres, sometimes even exceeding 6,000 metres. Thus the Pacific has an average depth of 4,028 metres; this average is greater than in any other ocean, the figure for the Atlantic being 3,332 metres. The following table showing the area of the floor at various depths for the Pacific is the work of Kossinna (1921) :— Deposits.—The deeper parts of the bed of the Pacific are covered by deposits of red clay (see OCEAN), which occupies an area estimated at no less than 105,672,000 sq.km., or three-fifths of the whole. Over a large part of the central Pacific, far removed from any possible land influences or deposits of ooze, the red clay region is characterized by the occurrence of manganese, which gives the clay a chocolate colour, and manganese nodules are found in vast numbers, along with sharks' teeth and the ear bones and other bones of whales. Radiolarian ooze is found in the central Pacific in a region between 15° N. to io° S. and 14o° E. to 15o° W., occurring in seven distinct localities and covering an area of about 3,000,00o sq.km. ; further, a wider strip of radiolarian ooze was discovered by the "Challenger" and the "Albatross," between 7° and 12° N. lat., stretching from 140° W. long. to the neighbourhood of the west coast of Central America, bringing the total area of the radiolarian ooze in the Pacific to about io,000,000 sq. kilometres. Between these two areas, almost on the Equator, a strip of globigerina ooze was found corresponding to the zone of globigerina in the equatorial region of the Atlantic. Globigerina ooze covers considerable areas in the intermediate depths of the west and south Pacific—west of New Zealand, and along the parallel of S., between 8o°-98° W. and 15o°-118° W.—but this deposit is not known in the north-eastern part of the basin. The total area covered by it is estimated at 30,000,00o sq.km.—about two-thirds of that in the Atlantic. Pteropod ooze occurs only in the neighbourhood of Fiji and other islands of the western Pacific, passing up into fine coral sands and mud. Diatom ooze has been found in a broad band between 57° and 67° S. lat., and thus in the Antarctic part of the Pacific, corresponding with its occurrence in the same lati tudes in the Atlantic and Indian oceans.