INTHODUCTION. 



While in charge of the expedition of the United States Fish Commission 

 Steamer "Albatross" during the winter of 1899-1900 we visited tlie coral 

 reef districts of the tropical Pacific, with the exception of the Sandwich, the 

 Samoan Islands, and the Galapagos. The Hawaiian Islands I had explored 

 on former occasions, and had also obtained a bird's-eye view of the reefs of 

 Samoa on my way to examine the Great Barrier Reef of Australia. 



It has thus been my good fortune to observe the structure of the great 

 majority of the coral reefs, atolls, and coral islands of the tropical Pacific, 

 and to have the benefit of the excellent charts published since the days of 

 Darwin and Dana. One cannot overestimate the great advantages to be 

 derived from recent surveys in studying groups of coral islands like the 

 Fiji or the Society Islands. The charts and " Sailing Directions " contain an 

 amount of information which no one individual could hope to bring together, 

 and their publication has made it possible for an observer ' to cover an 

 immense area and obtain within a reasonable time an insight into the 

 structure of the coral reefs of an oceanic realm like the Pacific. 



In this, as in preceding Reports, I have limited myself to an expo- 

 sition and explanation of the observations made in each of the coral reef 

 districts examined, and have only made such comparisons between the 

 various groups as seemed essential to the proper understanding of the 

 Report. 



These investigations on coral reefs date back to 1877; they have now 

 covered the principal coral reefs and islands of the Pacific, the West Indies, 

 and the Indian Ocean. The earlier reports were mainly descriptive, and 

 limited to statements that the facts observed did not seem to confirm 

 Darwin's theory of the structure and formation of coral reefs. As the work 



