ON THE FORMATION OF CORAL ISLANDS. 339 



Ocean. I may now however name one or two ex- 

 amples. Among these, Tongataboo is twenty leagues 

 in circumference, and is elevated ten feet above the 

 water. It would have been desirable to know the 

 thickness of this mass or bed of rock, but the sound- 

 ings have not been given. These are, however, 

 known to be deep, throughout all this sea ; since 

 they often exceed two and three hundred fathoms : so 

 that on any view the whole constitutes an enormous 

 bed of organic limestone. But the largest yet de- 

 scribed is the great reef on the east coast of New 

 Holland, which extends in an uninterrupted course 

 for three hundred and fifty miles ; forming, together 

 with others, a nearly continuous line of one thousand 

 miles or more in length, varying from twenty to fifty 

 miles in breadth. To form a just conception of such 

 a production, we should imagine it exposed from the 

 foundation ; it is a mountain ridge which will bear 

 comparison with many of the larger tracts of terres- 

 trial limestone in height ; as it far exceeds any that 

 are known, in the extent of its range. To him who 

 had not known such a production, viewing only the 

 coral itself, or the labourers in this work, it would 

 be incredible. It would be interesting to know the 

 height of this ridge from the bottom ; and hereafter 

 perhaps, some navigator, informed of that interest 

 attached to this subject which did not exist in the 

 time of Cook, or Flinders, or even of Kotzebue, 

 will enable us to form some estimate respecting it. 



The reefs, which are the germs of the islands, are 

 often disposed in a circular manner, or in other 

 curved or oval shapes : and I shall presently show 

 that this disposition is one of a singular ingenuity, as 

 it respects the form and character of the future 

 island. In other cases, they are simply grouped, with- 



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