288 Dr. Mac Culloch on the 
name, is an irregular oval of twenty leagues in circumference, 
while its elevation above the level of the water, reaches to ten feet. 
The soundings, from which the thickness of this bed of rock might 
be estimated, have not been given, but these are known to be 
deep throughout all this sea, and may safely be taken at not 
less than a hundred fathoms; so that the whole forms, what 
may be considered an enormous stratum of organic limestone. 
But the largest which appears to have been ascertained is the 
great reef on the east coast of New Holland, described by 
Flinders, which extends unbroken for a length of 350 miles; 
forming, together with others that are more or less separated 
from it, and from each other, a nearly continuous line of 1000 
miles, or more in length, with a breadth varying from twenty 
to fifty miles. Before such a mountain of limestone as this, 
even the Apennine almost shrinks in the comparison; and that 
such a mass should have been produced by such insignificant 
means, is a just subject of admiration to philosophical minds, 
and of wonder to those which have not considered the indefinite 
powers of units in endless addition. 
Although the greatest depths of these submarine moun- 
tains have not been ascertained, they have been sounded 
to 200 fathoms and more. It is not uncommon for navigators, 
to say that they lie in depths that are out of sounding: a vague 
mode of expression among mariners, as it is now known that 
the lead can be sent down without difficulty even to a thousand 
fathoms. The reefs, or the islands which they form, are some- 
_ times disposed in rows, or in lines more or less straight: at 
others, they are accumulated in groups ; and not unfrequently, 
they are disposed in a circular or oval manner; the latter dis- 
position, whether on the small or great scale, having a material 
influence on the form and nature of the future island. 
It is imagined, that their generation is very rapid; but on 
this part of the subject there is some uncertainty, while there 
is also reason to think that it has been somewhat exaggerated. 
These seas cannot, from their extent, be intimately known; nor 
is it possible that the infinite numbers of the reefs that exist in 
them should have been noted down. Even if they had, it is 
