DYNAMICAL GEOLOGY. 253 



in 1 896, had unfortunately to be given up on account of disasters 

 to the instruments. The expedition sent out from Sydney 

 University to the Funafuti Atoll under Professor Davis in 1897 

 was more successful, and the preliminary reports state that the 

 borer passed through 643 feet of reef limestone without reaching 

 the fundamental rock. But until the bore samples have been 

 examined microscopically no opinion can be formed regarding 

 the true nature of the limestone. Professor Agassiz visited the 

 Fiji group in 1897, and observed massive coral reefs more than 

 600 feet thick in several of the islands. As these reefs had been 

 elevated, Agassiz points out that the Pacific Ocean in the 

 vicinity of the Fiji Isles cannot be at present undergoing the 

 movement of subsidence assumed by Darwin and Dana, but 

 rather a movement of elevation, although these massive coral 

 reefs must have been formed during some foregoing period of 

 subsidence. 



Some of the most remarkable products of organic activity 

 are the hydrocarbon compounds which, in the form of asphalt, 

 naphtha, petroleum, impregnate sedimentary rocks belonging 

 to different geological ages. Fluid petroleum is usually 

 accompanied by greater or less quantities of inflammable gases, 

 while these may be absent in the rocks impregnated with 

 asphalt or other solid bitumen. Petroleum and naphtha 

 occur exclusively in deposits from salt-water, and very 

 commonly in loose sandy strata or in porous dolomitic and 

 calcareous rocks where these repose upon, and are succeeded 

 by, impervious shales. 



In Pennsylvania, Ohio, and Indiana, certain horizons of 

 the Silurian and Devonian formations contain enormous 

 quantities of petroleum and inflammable gases ; the naphtha and 

 petroleum wells at Baku on the Caspian Sea, and at Grosny on 

 the north side of the Caucasus, are apparently inexhaustible ; 

 and in Further India the so-called Rangoon oil has been 

 found in quantity. The Caspian, Caucasian, Roumanian 

 and Galician petroleum occurs in sandy strata of Oligocene 

 age ; both here and in Pennsylvania the oil is always in 

 greatest abundance at the crests of crust anticlines. 



During the last forty years geologists have rapidly advanced 

 our knowledge of the occurrences of these natural oils, but it 

 has been less easy to explain the process of their manufacture 

 in nature over extensive areas. Berthelot, the chemist, 

 suggested (1866) that they were produced when water with 



