NATURE 



[July 26. 1900 



,The secund terrace varies in height from 50 to 60 feet, the 

 third from 90 to 100 feet. The second terrace is deeply under- 

 cut ; and in the higher vertical cliffs extendihg into the third 

 terrace from the sea, the former positions of the terraces are 

 usually indicated by lines of caverns. 



From Niue we went to the Tongas, which we found a most 

 int,eresting group. The eleyated Tertiary coralliferous lime- 

 stones take here their greatest development, and are on a. scale 

 far beyond that of their development' in the Lau Group of the 

 Fijis, or the Paumotus. The first island of the Tongas we 

 visited, Eua, is perhaps the most interesting of the islands 

 composed of Tertiary elevated coralliferous limestone I have 

 visited. From Dana's account of it, evidently given at second 

 hand, I expected to find an island somewhat like Viti" Levu on 

 a very much smaller scale. But as we steamed up to it from 

 the east there could be no mistaking the magnificent face of 

 nearly vertical limestone cliffs forming the whole eastern, face 

 of the island, and at points rising to over a thousand feet in 

 height. At all projecting points lines of terraces were plainly 

 marked : at the northern point three could be followed, and at 

 the southern extreniity five, with traces of a sixth perhaps. 



Upon rounding the southern extremity of the island we 

 could see that* the island was composed of two ridges, running 

 north, separated by a deep Valley, the western ridge being 

 much lower than the easte.rn, not rising to a greater height 

 than a little over 500 feet. The western ridge is also com- 

 posed of limestone, and at the headlands we could trace three 

 terraces. 



We anchored at English Roads, opposite the outlet of ^he 

 drainage of the interior basin, where a small river has cut its 

 way through a depression in the shore terrace. On landing we 

 followed the crest of t)ie western ridge for a few miles and 

 could see the whole valley forming the basin of the island 

 lying between the two ridges, at our feet. Nothing coi^ld show 

 more clearly that such an island was not an elevated atoll, but 

 a plateau which had been eroded and denuded for a long period 

 of time by atmospheric and other agencies. 



To the westward of the Tonga Islands is a line of volcanic 

 islands extending nearly 200 miles, at a distance of from 15 to 

 20 miles parallel with the trend of the four irregularly-shaped 

 plateaux upon which rise the Tonga Islands. 



. The Tonga-Tabu plateau ig separated from the Namuka Group 

 plateau by a funnel-shaped channel with a depth passing rapidly 

 into 300 fathoms fr9m the lOO-fathom line. The Namuka 

 plateau is rectangular ; its principal island is Namuka, where we 

 anchored. 



This part of the Tongas is, li^ce the Lau Group in Fiji, made 

 up of islands in part volcanic and in part composed of elevated 

 coralliferous limestone. 



The Haapai plateau is triangular, with isolated islands rising 

 on the north-western side from the deep water separating it from 

 the Vavau plateau. On the northernmost plateau of the broad 

 ridge of the Tonga Islands is the Vavau Group, by far the most 

 picturesque of the Tonga Islands. Several parts of the island 

 of Vavau, as at the entrance to the harbour of Neiafu, and at 

 Neiafu, are finely terraced ; four terraces are indicated there, 

 and other flat-topped smaller islands show traces of two or three 

 terraces. The northern edge of Vavau Island rises to a height 

 of more than 500 feet, and slopes in a general way southward and 

 inland. The southern shore is deeply indented by bays and 

 sounds, and flanked by innumerable islands and islets, some of 

 considerable height (150 to 250 feet) which gradually become 

 smaller and smaller as they rise towards the southward and east- 

 ward, these islands having been formed from the denudation and 

 erosion of the greater Vavau. They form tongues of land and 

 sea and sounds of all shapes and sizes, showing the traces of the 

 former land-connections of the islands and islets, and their disin- 

 tegration on the eastward and southward by the. action of the sea. 



It is evident that in the Tonga Group, which is a very exten- 

 sive area of elevation, the recent corals have played no part in 

 the formation of the masses of land and of the plateau of the 

 Tonga Ridge, and that here again, as in the Society Islands and 

 the Cook Islands, both also in areas of elevation, they are a 

 mere ,thin living shell or crust growing at their characteristic 

 depths upon platforms which in the one case are volcanic, in the 

 other calcareous, the formation of which has been independent 

 of their growth. 



After leaving Suva we steamed to Funafuti, stopping on the 



way at Nurakita, the southernmost of the Ellice Islands. I 



was, of course, greatly interested in my visit of Fi^nafuti, where 



a boring had been made under the direction of a committee of 



NO. 1604, VOL. 62] 



the Royal Society, in Charge of Prof. David, of Sydney, after 

 the first attempt under Prof. SoUas had failed. The second 

 boring reached a depth of more than 1 100 feet. This is not the 

 place to discuss the bearing of the work done at Funafati, as 

 beyond the fact of the depth reached we have as yet no final 

 statement by the committee of the interpretation put upon the 

 detailed examination of the core obtained, and now in the hands 

 of Prof. Judd and his assistants. In addition to the above- 

 named islands, we also examined Nukufetau, another of the 

 Ellice Group. 



After leaving Nukufetau we encountered nothing but bad 

 weather, which put a stop to all our work until we arrived 

 under the lee of Arorai, the southernmost of the Gilbert Islands. 

 On our way from Tapateuea we steamed to Apamama and 

 Maiana, which we examined, as well as Tarawa. We next 

 examined Maraki. Both Maraki and Taritari, the last island 

 of the Gilberts which we examined, are remarkable for the de- 

 velopment of an inner row of islands and sand-bars in certain 

 parts of the lagoon piarallel to the outer land- rim, a feature 

 which also exists in many of the Marshall Islands atolls. 



We spent about three- weeks in exploring the Marshall 

 Islands, taking in turn the atolls of the Ralick Chain to the 

 north of Jaluit : Ailinglab Lab, Namu, Kwajalong and Ron- 

 gelab ; and then the atolls of the Ratack Chain : Likieb, Wotje 

 and Arhno. The atolls of the Marshall Group are noted for ' 

 their great size and the comparatively small area of the outer 

 land-rims, the land-rims of some of the atolls being reduced to 

 a few insignificant islands and islets. In none of the atolls of 

 the Ellice, Gilbert or Marshall Islands were we able to observe 

 the character of the underlying base which forms the foundations 

 of the land areas of these groups. In this respect these groups 

 are in striking contrast to the Paumotus, the Society Islands, 

 the Cook Group, Niue, the Tongas, and the Fiji Islands, where 

 the character of the underlying foundations of the land- rims is 

 readily ascertained. But, on the other had, these groups give 

 us the means of studying the mode of formation of the land-rims 

 in a most satisfactory manner, and nowhere have we been able 

 to study as clearly the results of the various agencies at work in 

 shaping the endless variations produced in the islands and islets 

 of the different atolls by the incessant handling and rehandling 

 of the material in place, or of the fresh material added from the 

 disintegration of the sea or lagoon faces of the outer land, or of 

 the corals on the outer and innef slopes. It has been very in- 

 teresting to trace; the ever- varying conditions which have resulted 

 in producing so many variations in the appearance and structure 

 of the islands and islets of the land -rims of the different groups. 



The boring at Funafuti will show us the character and age of 

 the rocks underlying the mass of recent material of which the 

 land-rim, not only of that atoll, but probably also that of the 

 other atoJIs of the group and of neighbouring groups, is com- 

 posed, though, of course, we can only judge by analogy of the 

 probability of the character of the underlying base from that of 

 the nearest islands of which it has been ascertained. When we 

 come to a group like the Marshalls, we have as our guide only 

 the character of the base rock of the islands of the Carolines, 

 which is volcanic ; while Naru and Ocean Islands, to the west 

 of the Gilberts and to the south-west of the Marshalls, indicate 

 a base of ancient Tertiary limestone. 



The Marshall Islands, as well as the Ellice and Gilbert, seem 

 to be somewhat higher than the Paumotus ; but this difference 

 is only apparent, and is due to the difference in the height of 

 the tides, which is very small in the Paumotus, while in these 

 groups it may be five and even six feet. 



From Jaluit we visited among the Carolines, the islands and 

 atolls of Kusaie, Pingelap, Ponapi, Andema, Losap, Namu, 

 the Royalist Group, Truk and Namonuito, obtaining thus an 

 excellent idea of the character of the high volcanic islands of 

 the group from our examinations of Kusaie and of Ponapi, 

 while the others represent, the conditions of the low atolls, 

 having probably a volcanic basis, but this was not observed at 

 any of those we examined. , .,. ^ 



The reefs of the volcanic islands of the Carolmes are similar | 

 in character to those of the Society Islands, though there are 

 some features, such as the great width of the plattorms of sub- 

 marine erosion of Ponapi and of Kusaie, and the development 

 of a border of mangrove islands at the base of the volcanic 

 islands, which are not found in the Society Islands. 



The Truk Archipelago was perhaps the most interesting of 

 the island groups of the Carolines, and it is the only group of 

 volcanic islands. surrounded by an encircling reef that I have 

 thus far seen in the Pacific which at first glance lends any 



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