Vol. 8, 1922 
GEOLOGY: W. M. DA VIS 
7 
CORAL REEFS OF THE LOUISIADE ARCHIPELAGO 
By W. M. Davis 
Harvard University 
Communicated November 19, 1921 
The Louisiade archipelago, consisting of four medium-sized and many 
small islands east of Newr Guinea, is v^ell represented on British Admiralty 
chart 2124 on a scale of about 1:280,000; chart 1477 shows part of the 
archipelago in greater detail on a scale of about 1 : 140,000. According to 
brief accounts by Macgillivray,^ Thomson,^ and Maitland,^ the chief 
islands are composed of steeply inclined and deeply eroded schists and 
.slates, traversed by quartz veins; they are evidently parts of the moun- 
tain range that extends for hundreds of miles along the northern coast of 
Nev^ Guinea, from which they have been separated by strong subsidence 
after having been eroded to about their present form. The largest island 
is Tagula, 30 miles in length east-west along the trend of its schists, and 8 
or 9 miles in width ; it has an embayed shore line and rises in 10 summits to 
heights of from 1330 to 2645 feet. Near by is the Calvados chain of satel- 
lite islands, which begins about 7 miles north of the middle of Tagula and 
extends 70 miles westward; it includes more than a score of members, 
the largest having a length of 11 miles and a height of 1110 feet. Tagula 
and its chain of satellites are enclosed by a superb barrier reef, the irreg- 
ularly oval circuit of which measures 112 miles in east- west diameter by 
about 30 miles north-south; it is unquestionably one of the finest 
reefs of its kind in the whole Pacific. 
The smaller islands of Rossel to the east and Deboyne to the northwest 
of Tagula are also surrounded by sea-level reefs, partly as fringes but mostly 
barriers. Misima, north of Deboyne, measuring 22 by 10 miles and reach- 
ing 3500 feet in height, is peculiar in having no sea-level reefs and in de- 
scending rapidly into deep water, altho it is terraced by unconformable 
reefs at various altitudes. It has therefore suffered a recent uplift after 
having previously taken part in the subsidence which characterizes the 
other islands; but its subsidence must have been more rapid than theirs 
as it has no widely developed barrier-reef lagoon floor, either near present 
sea level or above or below it. 
The Tagula barrier reef and its great lagoon merit special attention 
from the evidence that they give regarding the verity of certain coral-reef 
theories. The reef is best developed around the southeastern or wind- 
ward half of its great oval circuit, where it is interrupted by only 4 passes 
in a curved distance of 110 miles, and where the reef fiat has a width 
of 2 or 3 miles. The northwestern or leeward half of the barrier is 
strikingly discontinuous and consists in part of small patches, but more 
