[ 01 ] 



SECTION V. 



THE GEOLOGY OF FUNAFUTI. 



By Professor T. W. Edgeworth David, B.A., F.R.S., and G. Sweet, F.G.S. 



[See Plates 1-19.] 



As regards scale, tlie maps have been reduced to, as nearly as j)ogslble, 400 feet 

 (121*95 metres) to the inch. An actual scale in feet and metres is reproduced on 

 each map, so that if any slight error exists in the reduction of them by photo- 

 lithography or through subsequent shrinkage, such error corrects itself through the 

 scale having ^participated in the deviation of the map from the uniform standard. 



As regards the scope of the work, the geological boundaries have been drawn only 

 down to the level of low- water spring tides ; no attempt, for example, has been made 

 to show the boundaries of the great submarine sheet of Halimeda sand which forms 

 the floor of all the deeper portions of the lagoon. 



Reference to the index sheet Plate 1 will show that we have omitted from the 

 map some portions of the atoll rim which are distant from any islets, as, for example, 

 the portion north of the islet of Fuagea and intervening between it and Fuafatu, and 

 the long stretch of reef between Pava and Mulitefala. The total proportion of the 

 atoll rim thus omitted from the geological maps is about one~fifth of the whole 

 circumference. 



As regards the method of mapping, we took as our basis for the general outline 

 and orientation of the islets the British Admiralty Chart, No. 2983, compiled from 

 surveys by Captain A. Mostyn Field, R.N. The details shown on the geological 

 maps were filled in from our own traverses, made chiefly by pacing (in some cases by 

 chaining) and measuring angles witli a prismatic compass, the traverses in most cases 

 being checked at least once. The portion of the reef shown on Plate 17 was, 

 liowever, measured with a tape by Mr. A. E. Finckh, while the positions of the 

 permanent marks opposite the main diamond-drill bore, on the main island, both on 

 the ocean and lagoon sides (see Plate 19), were chained by Mr. G. H. Halligan", 

 as also were the distances between Professor Sollas's Nos. 1 and 2 diamond-drill 

 bores and the main diamond-drill bore. In tlie case of the section shown on Plate 17 

 the levels were taken by Mr. G. H. Halligan, with a 12-inch dumpy-level. In 

 other cases, however, the levels upon which the num.erous geological sections are based 

 were made by sighting from the object whose level was to be determined to the 

 horizon line of the ocean, noting where this line intersected the levelling staff held at 



