'oD< 



NATURE 



[August 7, 1890 



■therefore, by way of introduction, they are here briefly reviewed. ^ 

 The system of trends in feature-lines takes new significance from 

 a bathymetric map, for the courses are no lono[er mere trends of 

 islands or emerged mountain peaks ; they are the trends of the 

 great mountain ranges themselves ; and, in the Pacific, these 

 mountain courses are those of half a hemisphere. Some of the 

 deductions from such a map are briefly as follows : — 



(i) Over the Pacific area there are no prominent north-and- 

 south, or meridional, courses in its ranges, and none over the 

 Atlantic, except the axial range of relatively shallow water in the 

 South Atlantic. And to this statement it may pertinently be 

 added that there are none in the great ranges of Asia and 

 Europe, excepting the Urals ; none in North America ; none in 

 South America, excepting a part of those on its west side. 



(2) The ranges in the Pacific Ocean have a mean trend of not 

 far from north-west-by-west, which is the course very nearly of 

 the longer diameter of the ocean. One transverse range crosses 

 the middle South Pacific — the New Zealand— commencing 

 to the south in New Zealand and the islands south of it, with 

 the course N. 35° E., and continuing through the Kermadec 

 Islands and the Tonga group, the latter trending about N. 22° 

 E., and this is the nearest to north and south in the ocean, 

 except toward its western border. 



(3) The oceanic ranges are rarely straight, biit, instead, 

 change gradually in trend through a large curve or a series of 

 curves. For example, the chain of the central Pacific becomes, 

 to the westward, north-north-west ; and the Aleutian range and 

 others off the Asiatic coast make a series of consecutive curves. 

 Curves are the rule rather than the exception. Moreover, the 

 intersections of crossing ranges, curved or not, are in general 

 nearly rectangular. 



(4) Approximate parallelisms exist between the distant 

 ranges or feature-lines; as (i) between the trend of the New 

 Zealand range and that of the east coast of North America ; 

 and also that of South America (which is continued across the 

 ocean to Scandinavia) ; also (2) between the trend of the foot of 

 the New Zealand boot with the Louisiade group and New 

 Guinea farther west, and the mean trend of the islands of the 

 •central Pacific both south and north of the equator, and also 

 that of the north shore of South America. These are a few 

 examples out of many to be observed on the map. 



(5) The relatively shallow-water area which stretches across 

 the North Atlantic from Scandinavia to Greenland— the Scan- 

 dinavian plateau, as it may well be called — is continued from 

 these high latitude seas south-westward, in the direction of the 

 axis of the North Atlantic (or parallel nearly to the coast of 

 eastern North America and the opposite coast of Africa), and 

 becomes the " Dolphin Shoal." 



It may be a correlate fact in the earth's system of features that 

 a Patagonian plateau stretches out from the Patagonia coast, or 

 from high southern latitudes, in the direction of the longer axis 

 of the Pacific, and embraces the Paumotu and other archipelagos 

 beyond.^ 



The above review of the earth's physiognomy, if accompanied 

 by a survey of the map, may suffice for the main purpose here in 

 view : to illustrate the general truths — that system in the feature- 

 lines is a fact ; that the system is world-wide in its scope ; and 

 — since these feature-lines have been successively developed with 

 the progress of geological history — that the system had its 

 foundation in the beginning of the earth's genesis and was 

 developed to full completion with its growth. 



II, Facts Bearing on the Origin of the Deep-sea 



Troughs. 

 In treating of this subject, the facts from the vicinity of 

 volcanic lands that favour a volcanic origin <irQ first mentioned ; 



1 This subject of the system in the earth's feature-lines is presented at length, 

 with a map, in my Expedition Geological Report, pp. 11-23 and 414-424 ; and 

 also more briefly in the American Journal of Science, II. ii. 381, 1846. 



2 As parallelisms may have importance that is not now apparent, I draw 

 attention to one between the Mediterranean Sea that divides Europe from 

 Africa, and the West India (or West Mediterranean) sea that divides North 

 from South America. Both have a.n eastern, middle, a.nd western deep basin. 

 Their depths (see map) in the East Mediterranean, are 2170, 2040, and 1585 

 fathoms ; in the West Mediterranean (the three being the Caribbean, the 

 West Caribbean or Cuban, and the Gulf of Mexico), 2804, 3428, and 2080 

 fathoms. Further, in each Mediterranean Sea, a shallow-water plateau 

 extends from a prominent point on the south side, northward, to islands 

 between the eastern and middle of the deep basins ; one from the north-east 

 angle of Tunis to Sicily, the other from the north-east angle of Honduras to 

 Jamaica and Haiti, the two about the same in range of depth of water. 

 And this last parallelism has its parallels through geological history, even to 

 the Quaternary, when the great Mammals made migrations to the islands in 

 eachyrom the continent to the south. 



secondly, those from similar regions that are not favourable to 

 such an origin ; thirdly, facts from other regions bearing on the 

 question. 



A. Facts apparently favouring a Volcanic Origin. 



1. The Pacific soundings have made known the existence of 

 two deep-sea depressions, if not a continuous trough, within 

 forty miles of the Hawaiian Tsland; ; one situated to the north- 

 east of Oahu, or, north of Molokai, with a depth of 3023 

 fathoms, or 18,069 feet, and the other east of the east point of 

 Hawaii, 2875 fathoms, or within 750 feet of 18,000 feet. 

 Again, 450 miles north-east of Oahu, there is a trough in the 

 ocean's bottom, over 800 miles long, which runs nearly parallel 

 with the group and has a depth of 3000 to 3540 fathoms ; 

 and, as far south, another similar trough of probably greater 

 length has afforded soundings of 3000 to 3100 fathoms. The 

 depths about the more western part of the Hawaiian chain of 

 islands have not yet been ascertained, and hence the limits of 

 the deep areas are not known. Such depths, so close to a line 

 of great volcanic mountains, the loftiest of the mountains not 

 yet extinct, appear as if they might have resulted from a sub- 

 sidence consequent on the volcanic action. 



The subsidence might have taken place (l) either from 

 underminings — which the amount of matter thrown out and 

 now constituting the mountain chain, with its peaks of 20,000 

 to 30,000 feet above the sea-bottom, shows may be large ; or 

 (2) from the gravitational pressure in the earth's crust, about a 

 volcanic region which speculation makes a source of the ascen- 

 sive force and of the upward rising of the lavas, the sub- 

 siding crust following down the liquid surface beneath. In 

 either case the mass of ejected material might be a measure 

 more or less perfectly of the maximum amount of subsidence. 



2. In the western part of the North Pacific, at the south 

 end of the volcanic group of the Ladrones off the largest island 

 of the group, Guam, the Challenger found a depth of 4475 

 fathoms, one of the two deepest spots yet known in the Pacific. 

 The situation with reference to the group is like that off the east 

 end of the Hawaiian group, 



3. East of Japan and the Kuriles, a region of ranges of vol- 

 canoes, there is the longest and deepest trough of the ocean, 

 the length 1800 miles, the depths 4000 to 4650 fathoms ; and 

 farther north-east, south of one of the Aleutian Islands, a depth 

 of 4000 fathoms occurs again; and depths of 3100 to 3664 

 fathoms also still farther east. It is probable that the 4000- 

 line trough continues from the Kurile to this deep spot off the 

 Aleutian volcanic range ; and if so, the length of the trough 

 is over 2500 miles. The map is made to suggest its extension 

 still farther eastward ; but among the very few soundings made, 

 none below 3664 fathoms have yet been obtained off the more 

 eastern Aleutians. 



Other similar facts may be found on the map ; and still 

 others may exist which are not now manifest owing to the 

 sinking of oceanic areas and islands. But no cases can be 

 pointed to which are more decisively in favour of volcanic origin. 



B. Facts ft cm the Vicinity of Volcanic Regions apparently not 

 referable to a Volcanic Origin. 



The ocean off the western border of North and South 

 America affords striking examples of the absence of deep 

 troughs from the vicinity of regions eminently volcanic. The 

 South American volcanoes are many and lofty ; and still the 

 ocean adjoining is mostly between 2000 and 2700 fathoms in 

 depth ; and just south of Valparaiso, it shallows to 1325 

 fathoms. The only exception yet observed is that of a short 

 trough of 3000 to 3368 fathoms close by the Peruvian shore. 

 It may, however, prove to be a long trough, although certainly 

 stopping short of Valparaiso. The waters, however of the 

 Pacific border of America deepen abruptly compared with 

 those of the Atlantic border ; and the significance of this fact 

 deserves consideration. 



The facts off Central America are more remarkable than 

 those off the coast to the south. The volcanoes are quite near 

 to the Pacific coast, and still the depths are between 1500 and 

 2500 fathoms. 



The condition is the same off the west coast of North Ame- 

 rica. Of the two areas of 3000 and over, nearest to the east 

 coast of the North Pacific, one is 600 miles distant in the lati- 

 tude of San Francisco, and the other is within 10° of the 

 equator and 20" of the coast ; both too far away to be a 

 consequence of volcanic action in California, Mexico, or 

 Central America. 



NO, 



1084, VOL. 42] 



