10 Transactions. 



unconformably contouring around the spur-ends of embayed coasts — witness 

 Palawan, the south-westernmost member of the PhiUppines, and many other 

 embayed islands in that group — well represented in recent charts of the 

 United States Coast and Geodetic Survey ; also the Andaman Islands, in 

 the Bay of Bengal ; for in all these examples the coast is elaborately 

 embayed ; and hence their fringing reefs must be unconformable, and 

 their submergence must have taken place at a faster rate than reef- 

 upgrowth. Many other examples of the same kind might be cited. 



Fringing Reefs and Submarine Platforms. — Fringing reefs thus assume 

 a much greater interest than is generally allowed to them : their relations 

 to the features of the coasts they border deserve close attention. The 

 breadth of the reefs should be noted as a means of estimating the time 

 that has elapsed since the last movement of submergence took place. 

 The ofi-shore soundings of reef-fringed coasts of submergence are also of 

 importance, for they frequently reveal a submarine platform that in all 

 probability represents a drowned barrier reef and its lagoon. 



Such submarine platforms, several miles in width, are found in 

 association with Palawan and the Andamans, although the sea-level 

 fringing reefs of these islands are narrow. A well-developed submarine 

 platform surrounds the greatly denuded " volcanic wreck " of Fauro, a 

 small island with narrow fringing reefs in the Solomon Group. A similar 

 platform is shown by the latest surveys of the United States Hydro- 

 graphic Office to surround the Samoan island of Tutuila ; but the fact 

 that the spur-ends of this island are rather strongly clified behind their 

 fringing reefs distinguishes it from the other examples named. Submarine 

 platforms occur around the Marquesas Islands also ; but here, although 

 the spur-ends are cliff ed, as in Tutuila, they are not fronted by fringing 

 reefs. 



The depth of the submarine platforms ofi reef-fringed shores is not 

 constant : along the west coast of Palawan the platform varies in depth 

 from 25 or 30 fathoms near its southern end to 60 fathoms near its mid- 

 length ; the Fauro platform has depths of 70 or more fathoms ; the 

 Andaman platform is 30 or 40 fathoms in depth. On the other hand, 

 part of the coast of Samar, in the Philippines, facing the open Pacific, 

 has fringing reefs around its headlands, but its submarine slope descends 

 rapidly to great depths. Now, let it be noted, first, that the three 

 chief elements of the fringing-reef problem as here considered — duration 

 of the pre-submergence period of subaerial erosion, rate and amount of 

 submergence, and duration of post-submergence period of fringing-reef 

 growth — have unlike values on difl'erent islands ; secondly, that many 

 other islands have well-developed barrier reefs which suggest slow sub- 

 mergence, and that some barrier reefs are broad and others are narrow, 

 thus suggesting that the rate and date of their submergence are unlike ; 

 and, thirdly, that many elevated reefs occur at difterent altitudes and in 

 different stages of erosion. 



It thus becomes evident that the history of various reef-encircled 

 islands must consist of unlike sequences of movements and pauses. 

 Hence local movements of the reef - formations themselves, which may 

 varv greatly, explain the varied facts much better than changes of ocean- 

 level, which must everywhere be of the same rate, date, and amount. In 

 order to learn how greatly the values of the various elements differ from 

 place to place, their value for every coast should be determined 

 independently. One of the most important of these elements is the 



