540 W. D. SMITH GEOLOGIC INFLUENCES IN THE PHILIPPINES 



of acid gases and ashes from Taal Volcano in 1911 destroyed the orange 

 crop — the principal industry of that section — for that year, in the suc- 

 ceeding years increased yields were given. Still a third compensation is 

 the great number of hot springs of medicinal and saline waters which 

 furnish the people with remedies and with salt for their food. 



Coral Eeeps 



There are two dominant formations to be found in or about most 

 Pacific islands, in Oceania especially. These are volcanic ejecta and 

 coral, and both are intimately bound up with the life and economy of the 

 peoples inhabiting that part of the world. Some Pacific islands are all 

 volcanic, some all coral, and many are made up of both kinds of for- 

 mations. 



Coral formations are extensive in the Philippines — the Coast and Geo- 

 detic charts show to what extent — about 65 per cent of the coast lines of 

 the archipelago having been surveyed. 



This subject alone would provide material for a very ample paper or 

 even a book. It is not necessary to go into the subject of the origin of 

 coral reefs, but a few facts about the growth of coral might not be without 

 interest, especially those points relating to the influence of the coral for- 

 mations on the life of the peoples living near them. 



As Becker^^ and others have pointed out, there are several benches or 

 raised coral reefs on some of the Philippine coasts, particularly those of 

 northwest Luzon ; and on the island of Cebu it is possible to go from the 

 living reef on the coast inland to nearly 3,000 feet elevation on continuous 

 coral reef formations. N"ot much can be contributed here about the con- 

 tact of these reefs with the underlying rock because of the lack of good 

 sections in favorable places and also for the reason that the writer was 

 not looking for this sort of thing when in the neighborhood, being con- 

 cerned principally with economic questions. However, in a few places the 

 reefs were found to make an unconformable contact with eroded igneous 

 rock beneath. In many parts of the islands the coral grows close to shore, 

 with no gap between — that is, the latter joins snugly onto the former. 



As would be expected, the top of coral reefs is a fairly flat platform, 

 the limiting plane being the level of the sea. The outer edge is rather 

 an abrupt slope dipping off into deep water. The surface has more or 

 less numerous holes in it which are filled with water. Opposite the 

 mouths of debouching streams there are, almost without exception, open 

 channels, the current and the influx of fresh water both being deleterious 

 to the coral polyp. 



^ G. P. Becker : Twenty-fii-st Annual Report, U. S. Geological Survey, 1901. 



