4 PREFACE. 
the origin of the included channels and lagoons, and of the 
distribution of reefs, together with a review of the facts with 
reference to their geological bearing. 
The observations forming the basis of the work were made 
in the course of the cruise of the Wilkes Exploring Expedi- 
tion, around the world, during the four years from 1838 to 
1842. The results then obtained are published in my Report 
on Zodphytes, which treats at length of Corals and Coral 
Animals, and in a chapter on Coral Reefs and Islands form- 
ing part of my Geological Report. 
The opportunities for investigations in this department. 
afforded by the Expedition, were large. We visited a number 
of the coral islands of the Paumotu Archipelago, to the north 
of east from Tahiti; also, some of the Society, Navigator, and 
Friendly Islands, all remarkable for their coral reefs; the 
Feejee Group, one of the grandest regions of growing corals 
in the world, where we spent three months; several islands 
north of the Navigator and Feejee Groups, including the Gil- 
bert or Kingsmill Group; the Sooloo sea, between Borneo 
and Mindanao, abounding in reefs; and, finally, Singapore, 
another East India reef-region. 
Most agreeable are the memories of events, scenes and 
labors, connected with the cruise:—of companions in travel, 
both naval and scientific; of the living things of the sea, 
gathered each morning by the ship’s side, and made the study 
of the day, foul weather or fair; of coral islands with their 
groves, and beautiful life, above and within the waters; of 
exuberant forests, on the mountain islands of the Pacific, 
where the tree fern expands its cluster of large and graceful 
fronds in rivalry with the palm, and eager vines or creepers 
intertwine and festoon the trees, and weave for them hangings 
of new foliage and flowers ; of lofty precipices, richly draped, 
