H6 
GEOLOGY: W. M. DAVIS 
extent which would appreciably affect the results. With the polarimetric 
apparatus at present at our disposal it will be possible to work with con- 
siderably smaller salt concentrations and to reduce the concentration 
of the reference substance as low as 0.01 molal in the case of Hthium 
chloride solutions. By substituting trehalose for raffinose it will prob- 
ably even be possible to use a considerably lower concentration than 
this and thus to remove all doubt as to the vaHdity of the assumption 
in question. Work along these lines will be continued in this laboratory. 
A more complete description of the research described in this paper 
will soon appear in the Journal of the American Chemical Society. A 
detailed description of it has already been printed as part of a doctor's 
thesis submitted by Earl B. Millard to the Graduate School of the 
University of Illinois. 
1 Washburn, /. Amer. Chem. Soc, 31, 322 (1909). 
^ Buckbock, Zs. physik. Chem., 55, 563 (1906). 
THE ORIGIN OF CORAL REEFS 
By W. M. Davis 
DEPARTMENT OF GEOLOGY AND GEOGRAPHY. HARVARD UNIVERSITY 
Presented to the Academy, January 7,1915 
A Journey across the Pacific. A liberal grant from the Shaler Me- 
morial Fund of Harvard University, supplemented by a subsidy from the 
British Association for the Advancement of Science, whose meeting 
in Australia during August I was invited to attend as a foreign guest, 
enabled me to spend the greater part of the year 1914 in visiting a 
number of islands in the Pacific Ocean with the object of testing the 
various theories that have been invented to accoimt for coral reefs. 
Thirty-five islands, namely, Oahu in Hawaii, eighteen of the Fiji group, 
New Caledonia of which the entire coast line was traced, the three 
Loyalty islands, five of the New Hebrides, Rarotonga in the Cook group, 
and six of the Society islands, as well as a long stretch of the Queensland 
coast inside of the Great Barrier reef of northeastern Australia, were 
examined in greater or less detail. Darwin's theory of subsidence is, 
in my opinion, the only theory competent to account for the coral reefs 
there seen; thus my work leads to the same conclusion as that reached 
by several other recent students of this old problem. A full discussion 
of my observations will be published later, probably in the Bulletin of 
the Museum of Comparative Zoology at Harvard College. A brief 
statement of the chief results gained here follows. 
