FORMATION OF CORAL REEFS. 149 
figuration of our globe, as the sinking of lands 
beneath the ocean, or the gradual rising of con- 
tinents and islands above it, — or the wearing of 
great river-beds, or the filling of extensive water- 
basins, till marshes first and then dry land suc- 
ceeded to inland seas,—or the slow growth of 
coral reefs, those wonderful sea-walls raised by 
the little ocean-architects whose own bodies fur- 
nish both the building-stones and the cement 
that binds them together, and who have worked 
so busily during the long centuries, that there 
are extensive countries, mountain-chains, islands, 
and long lines of coast consisting solely of their 
remains, —or the countless forests that must 
have grown up, flourished, died, and decayed, 
to fill the storehouses of coal that feed the fires 
of the human race to-day,—if we consider all 
these records of the past, the intellect fails to 
grasp a chronology for which our experience 
furnishes no data, and the time that lies behind 
us seems as much an eternity to our conception 
as the unknown future that stretches indefinitely 
before us. 
The physical as well as the human history of 
the world has its mythical age, lying dim and 
vague in the morning mists of creation, like that 
of the heroes and demigods in the early tra- 
ditions of man, defying all our ordinary dates 
and measures. But if the succession of periods 
