AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 115 



reefs, the weather, or the leeward edges, on the inner lines of reef 

 patches. 



The scene he figures as resulting in the wreckage of the fringing reef 

 by a hurricane on Saddleback Island (Plate XXXI.) has nothing in 

 common with the existence of " nigger heads " occurring on the edges 

 of the reef flats, which are, as I think can be conclusively shown, the 

 remnants left from the erosion of a much larger mass, as suggested by 

 Jukes. 



A little farther north, the condition of things existing at Two Isles 

 is similar to that described at Three Isles. We find the same coarse 

 beach rock and the negro heads remaining from the eroded elevated 

 conglomerate; the coral reef flat connecting the islands forms an ir- 

 regular lagoon, enclosed on the northwest side by the islands and the 

 reef flat, and on the southern side by a somewhat deeper reef flat, from 

 which rise a few negro heads. We were struck with the great number 

 of dead Nautilus and Spirula shells thrown up on the sand beaches of 

 the Three and Two Isles groups. Also by the masses of cuttlefish 

 bones of all sizes which were found with them. These cuttlefish bones 

 could often be seen floating by us in great numbers. The accumulation 

 of such quantities of dead shells of Spirula, of Nautilus, and of Cuttle- 

 fish bones may give us a hint as to the mode of their accumulation in 

 former geological periods, and certainly show how poor a guide they are 

 of the character of the fauna of the district immediately adjoining the 

 place of deposit. 



The larger one of the Two Isles is a bank a few feet in height 

 thrown up from the sand derived from the disintegration of the elevated 

 beach rock flanking its side (Plate XXXIII.). 



The Rocky Islets, South and North Direction Islands, and the Liz- 

 ard Islands are among the best examples of rocky islets left as remnants 

 of the former eastern extension of the Australian mainland. The south- 

 ern of the Rocky Islets, with its bare rounded summit, shows admi- 

 rably the extent of the denudation and erosion to which the islands of 

 this part of the Australian continent have been subjected. Extending 

 towards the southern islet a small reef flat has been formed from the 

 extremity of the larger central island ; a still smaller flat extends from 

 the opposite extremity (Plate XXXIV.). 



Lizard Island (Plates XXL, XXIL), as also the Direction and Rocky 

 Islets, show wonderfully well, not only the great denudation and ero- 

 sion that has taken place, but also that which is now going on. Huge 

 masses of rock are pealing off in conchoidal fractures, and splitting up 



