190 DISTRIBUTION OF CORAL-REEFS. Ch. VI. 
subsiding areas on our map, as indicated by the pre- 
sence of atolls and barrier-reefs ; and of the rising or sta- 
tionary areas, as known by upraised organic remains, 
or inferred from the presence of fringing -reefs. — The 
immense surfaces seen on the map, which accord- 
ing to our theory, or from the plain evidence of up- 
raised remains, have undergone either a downward 
or upward change of level within a geologically late 
period, is a highly remarkable fact. The existence of 
continents shows that the areas which have been up- 
raised are immense. With respect to South America 
we may feel sure, and with respect to the western shores 
of the Indian Ocean we have reason to suspect, that 
this rising is either now actually in progress, or has 
taken place quite recently. By our theory, it may 
safely be inferred that the areas which have lately sub- 
sided are likewise immense ; or, judging from the earth- 
quakes now occasionally felt there, and from other ap- 
pearances, are still subsiding. The smallness of the 
scale of our map should not he overlooked ; each square 
on it containing 810,000 square miles. If we take the 
space of ocean from near the southern end of the Low 
Archipelago to the northern end of the Marshall Archi- 
pelago, — a length of 4,500 miles, we see that, as far as 
known, every island, excepting Metia, is atoll-formed. 
The eastern and western boundaries of our map are 
continents, and they are rising : the central areas of 
the great Indian and Pacific Oceans, are mostly sub- 
siding ; between them, north of Australia, lies the most 
broken land on the globe, and there the rising parts 
