AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 115 
reefs, the weather, or tho leoward edges, on tho inner lines of roef 
patehes. 
The scene ho 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 
ig similar to that described at Three Isles. We find the same coarse 
bench 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 
roof flat, and on the southorn side by a somewhat deeper roof flat, from 
which rise a few negro heads. Wo 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 à 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 dorived from the disintegration of the elevated 
beach rock flanking its side (Plate XXXIII): 
Tho 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- 
orn of tho Rocky Islets, with its baro 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, XXII), as also the Direction and Rocky 
Islets, show wonderfully well, not only the great denudation and ero- 
sion that has taken place, but algo that which is now going on. Huge 
masses of rock are pealing off in conchoidal fractures, and splitting up 
