78 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
from the walls of the cracks and meeting in the center in a notched 
line, suggesting the “comb” structure in a mineral vein. 
75’. The rock contains meandrine organisms (probably “ghosts” of 
corals), altered Lithothamnion, Foraminifera, and echinid spines. All 
the organisms, with the exception of the echinid spines, are much 
dolomitized, and in many cases crystals of dolomite are incrusting the 
organisms. Between the organic fragments granular calcite occurs in 
large amount. The limestone was probably originally a fragmental 
rock, becoming subsequently highly dolomitized. After dolomitization 
the many spaces in the cavernous dolomite were filled with a clear 
mosaic of calcite. The echinid spines which had resisted dolomitization 
have received a secondary deposit of calcite round them in optical con- 
tinuity with the original organisms, 
30’. A similar rock to the last one described, but with the differ- 
ence that the proportion of dolomitized organisms to secondary calcite 
is much larger. A good deal of “ mud” also occurs as a matrix to some 
of the organisms. Particular interest centers in one of the organisms, 
a rather altered Orbitoides which could not be specifically identified. 
It goes to show, however, that the rock in which it occurs is not later 
than Miocene in age. 
Yaruata. — Yathata is one of the northern islands of the Lau group,! 
and is situated in latitude 17° 15’ 8., longitude 179° 30’ W. It rises 
to a height of 840 feet, and six well-marked terraces occur on its slopes. 
On the western side of the island a voleanic mass reaches the 500 feet 
level, scorching and whitening the limestone. 
Chemical. — The only specimen available was from near the summit 
of the island at a height of 800 feet. It consists of a highly dolomitic 
limestone, with 38.7 per cent. of magnesium carbonate. 
Calcium Magnesium 
Height. Carbonate. Carbonate. 
800’ 61.3 38.7 
Microscopical. — Among the organisms which formerly were present in 
large numbers, only Lithothamnion and Polytrema retain their struc- 
ture. The remainder are represented by dirt outlines, filled in with 
clear dolomite crystals. The matrix of the rock is a gray, partly crystal- 
line “ mud.” 
KamBara. — Kambara occurs at the southern end of the Lau group 
in latitude 18° 57!’ S., longitude 178° 55’ W. Its structure? is very 
1 Bull. Mus. Comp. Zodl., 1900, Vol. XX XVIII., p. 22. 
2 Bull. Mus. Comp. ZoGl., 1899, Vol. XXXIIL., p. 98. 
