xiv INTRODUCTION. 



comparatively limited field of Keeling, Tahiti, and Mauritius. Darwin's 

 theory was also adopted by Jukes, who had just completed a survey 

 of the Great Barrier Reef of Australia. The field covered by Dana 

 and Jukes thus seemed to include all that was essential to satisfy the 

 demands of Darwin's theory. 



The problems which have arisen from a more extended study of the 

 coral reefs since that time have greatly modified the views so gener- 

 ally held regarding their origin. A number of explorers in recent years 

 have attacked limited areas, and their conclusions have in nearly all 

 instances been opposed to Darwin's theory. It is unfortunate that so much 

 has been written on the subject of coral reefs by persons who have never 

 studied them in the field, and who have added to the bibliography of coral 

 reefs a mass of material which has done little or nothing towards the solu- 

 tion of the questions at issue. 



It may not be out of place to sketch rapidly the characteristics of the 

 coral reef groups of the Pacific. 



The Galapagos^ and Marquesas are not of special interest as far as coral 

 reefs are concerned. In both groups corals are limited to restricted shore 

 areas ; they do not even form fringing reefs ; they are mere patches in the 

 shallow bays cut into volcanic bluffs. 



In the Sandwich and Samoan Islands occur fringing reefs limited to 

 certain parts of the larger volcanic islands ; on the shores of other islands 

 they are either absent or reduced to mere patches. 



In the Sandwich Islands, Lysan, Lisianski, French Frigate Shoal, Maro, 

 Hermes, Cure, and Midwa,y Islands are atolls and coral reefs scattered along 

 the chain of volcanic islets extending to the westward of Kauai. Elevated 

 coralliferous limestones occur along the southern face of Oahu. On the 

 northern side asolian rocks attain a height of twenty to twenty-five feet 

 and the fringing reefs are underlaid by a base of elevated tertiary limestone 

 from which a reef flat platform has been eroded. 



In Samoa extensive fringing reefs and barrier reefs occur on Upolu. In 

 Savaii the east face is flanked by barrier reefs. In Tutuila, as in the islands 



1 At the Galapagos, during a deep sea expedition off the Panamic district, we found nothing of 

 importance regarding coral reefs. See also Darwin, Coral Reefs, p. 197. 



