THE GREAT BARRIER REEF 



311 



of the theory, therefore, assume the land to have been 

 higher at the time the corals began to grow, than at pre- 

 sent, so that the coast line then reached the line of the 

 outer reef b. As the land gradually sank, the corals 

 grew up, keeping pace with the incursion of the ocean, 

 finally producing the tremendous buttress of coral rock 



a. Sea outside the barrier, generally unfathomable. 



b. The actual barrier. 



c. Clear channel inside the barrier, generally about fifteen to twenty fathoms 

 deep. 



d. The inner reef. 



e. Shoal channel between the inner reef and the shore. 



F. The great buttress of calcareous rock, formed of coral and the detritus of 

 corals and shells. 



G. The mainland, formed of granites and other similar rocks. 



that overlies the sunken land, and stretches out from 

 the present shore line. 



Agassiz began the preparations for this expedition 

 months in advance, and every detail was most carefully 

 thought out and provided for. Indeed, he exercised 

 the same careful forethought in the organization and 

 equipment of all his cruises. Knowing the labor and 

 care necessary to arrange for what he called " one of 

 his own little trips," he was always amazed at the work it 

 must have required to fit out for such a voyage, for ex- 

 ample, as Nansen's exploration in the Fram. 



A small cargo steamer, the Croyden, was chartered 



