A. Agassiz — Great Barrier Reef of Australia. 243 



is an interesting problem. Such an eastern extension of this 

 subsidence and elevation would go far to explain the existence 

 of the banks, islands and archipelagos of the Southern Pacific 

 as formed by the denudation and erosion of a preexisting con- 

 tinent or continental islands. For if it has extended generally 

 over the Southern Pacific we could explain the formation of 

 coral reefs upon the remnants of these Pacific Lands much as we 

 have attempted to explain the presence of coral reefs off the 

 coast of Queensland and between it and ISTew Guinea. The 

 subsidence and elevation having both antedated the present 

 epoch, neither could have influenced the formation of the coral 

 reefs of our epoch or have been the cause of the peculiar shape 

 of the Atolls and Barrier Reefs of the South Pacific coral belt. 



We also have evidence of the most positive kind that there 

 has been an elevation of at least ten feet along the whole of 

 the littoral belt of Queensland and as far east as the outermost 

 edge of the Great Barrier Reef. Along the coast of the main- 

 land and on some of the islands close to it, this is shown by 

 the existence of a peculiar conglomerate first observed by 

 Jukes and subsequently by others at Cape Upstart, and at 

 other points of the Queensland coast. Farther east on some 

 of the islands between the mainland and the inner edge of the 

 barrier reef, the beach sand conglomerate is often elevated to 

 the same height as the shore conglomerate. Finally it can be 

 distinctly shown that the elevated shoi^e conglomerates and 

 beach rocks are merely outliers, indicating a more extensive 

 elevation in which the whole of the Great Barrier Reef dis- 

 trict was involved. Many of the inner reef fiats and some of 

 those close to the outer margin of the reef are edged with a 

 belt of so-called negro heads, huge masses of coral, the rem- 

 nants of the elevated coral reef which once flourished upon 

 these flats. The elevated reef having been eroded and worn 

 away left the outer flats generally covered with dead corals and 

 coral fragments, while the flats of the inner series of reefs are 

 usually fringed by a broad belt of large negro heads, the 

 latter not having been reduced with the rest of the elevated 

 reef of which they once formed a part. The surface of the 

 negro heads'^ is deeply pitted and honeycombed like the surface 

 of the elevated coral reefs of Florida and of the northern coast 

 of Cuba. 



One cannot fail to be struck with the immense amount 

 of silt held in suspension by the inner waters of the Great 

 Barrier Reef. The rivers during the floods bring down large 

 masses of deposit ; the flanks of the coast mountains as well as 



* As far as I know, Flinders was the first to apply the term of " negro heads " 

 to the remnants of the former elevated coral reef. The existence of such an 

 elevated reef suggested itself on reading his description. 



