CORAL CONGLOMERATE. 335 



which are found rapid currents, neither of which 

 affect the land. Before entering on any discussion, 

 as to the origin of the Barrier reef, I wish to refer 

 to the masses of coral conglomerate forming strips 

 of flat land along shore behind the present beaches, 

 and to the presence of pumice pebbles sometimes in 

 that conglomerate, but more usually scattered over 

 its surface loose upon the ground. I will also make 

 some observations on the structure and present con- 

 dition of Raine's Islet. 



The coral conglomerate has been already de- 

 scribed, especially that at Cape Upstart, and in the 

 Capricorn Group of islands. Flats composed of it, 

 half a mile in width, are frequent along the shore of 

 the north-east coast of Australia. It must either 

 have been formed under water, in which case its 

 existence as dry land proves elevation of the whole 

 coast, or it must have been produced by the piling 

 action of the surf heaping up successive accumula- 

 tions of calcareous sand, which has been subse- 

 quently compacted into rock. In the latter case, 

 it never could have reached a higher level than it 

 now has (a few feet above high water mark), and its 

 formation by this action must have required an im- 

 mense period of time, during the whole of which no 

 depression can have taken place. Upon all these flat 

 spaces formed of this conglomerate, as well as upon 

 all other flat land along the eastern and north-eastern 

 coast of Australia, which is not more than ten feet 

 above high water mark, there is found an abun- 



