rer rape 
AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 139 
southern edges of the laud mass (Plate 22). In Yangasd the south- 
eastern and western faces were probably the highest land of the group 
(Plate 22). 
Admiral Wharton’? has suggested “‘the cutting down of volcanic 
islands by the action of the sea, and that this action has a far greater 
share in furnishing coral foundations than has been generally admitted.” 
From our experience in Fiji we may safely modify this to the cutting 
down, not only of volcanic islands, but also of other elevated islands, 
and their cutting down not only by submarine erosion but also by 
denudation and atmospheric agencies, and thus preparing the founda- 
tions upon which recent corals have established themselves. Add to 
this the elevation of banks composed of volcanic rocks or of sedimentary 
rocks up to heights at which corals or corallines can begin to grow, 
and we have in addition to their increment in height from the increase 
due to pelagic organisms and the decay of other calcareous invertebrates 
living upon their surface all the elements needed for the preparation of 
a set of foundations from very different causes. 
I have already on other occasions called attention to the powerful 
scouring effect produced upon the interior of an atoll or lagoon, or the 
channel of a barrier reef, by the mass of water poured into it from all 
sides as the huge ocean swells break over the outer rim. This mass of 
water can find no outlet against the incessant swell ; it must escape to 
- leeward through the openings in the outer reef flats, or laterally over the 
low parts of their outer edges. It will be noticed that the openings are 
usually on the west face of the atoll, the direction in which the prevail- 
ing trades drive the water of the lagoon. The water becomes charged 
with particles of lime or of other material, and we soon have all the 
elements of a modified gigantic pothole, from which the churned mate- 
rial? is carried out by the currents flowing through the entrances into 
the lagoon. It has long been known that there is a violent rush of 
water out of the lagoons, the velocity attained reaching sometimes four 
to five knots. In Fiji I have noticed these powerful currents flowing 
out of the passages leading into the lagoons of Fulanga (Plate 22), of 
Ngele Levu (Plate 17), of Wailangilala (Plate 18), of Vatu Leile (Plate 9), 
of Totoya (Plate 23), and racing along the interior channels of the great 
1 “The Foundation of Atolls,” Nature, February 25, 1897, p. 891. 
2 Material derived mainly from the mechanical disintegration of the corals or 
substratum forming the surface of the reef, and also in part from the chemical dis- 
integration due to the sea water at work to rot and dissolve the limestones of the 
Teef. 
