30 CORAL FORMATIONS. 
much resembling those of the Pacific are to be found throughout the 
interior of our own country, constituting some of the beds of limestone 
that underlie the Western States; and over other parts of the world 
there are extensive strata of similar character and origin. Many in- 
teresting points in geology are consequently illustrated by the forming 
reef. ‘The polyp though among the lowest animals in organization, 
may therefore claim a place with the most efficient agents of change 
and progress in the geological history of the earth. 
In view of these considerations,—the simplicity of the means, the 
grandeur of the results, and the important bearing of the facts on 
science and commerce,—we shall be justified in much minuteness 
of detail in the following pages. In another volume, we have dwelt 
at length upon the structure and habits of coral animals, and en- 
deavoured to illustrate the manner in which coral is secreted, its 
relation to the polyp, and the source of the various forms which it 
assumes, besides giving full descriptions of species. In the following 
pages we present the subject with reference to the formation of reefs 
and islands. 
In treating of coral formations, we may first consider their actual 
condition and characters, as presented in existing seas; and next, the 
several causes, arising from the habitudes of polyps and different 
external agencies, by which their features have been produced, and 
their growth and distribution regulated. 
I. FEATURES AND STRUCTURE OF REEFS AND ISLANDS. 
1. GENERAL VIEW OF CORAL REEFS AND ISLANDS. 
The general features of reefs and coral islands have often been 
delineated by travellers, and are probably almost as familiar to the 
reader as the scenes of the land around us. Yet a few brief remarks 
on this point form a necessary introduction to the more minute descrip- 
tions of structure which follow.* 
* The features of coral islands and reefs were first particularly detailed by J. R. 
Forster, who accompanied Captain Cook in his second voyage. They have since been 
described by Kotzebue, Chamisso, Beechey, Quoy and Gaymard, Lutke, Stutchbury, Eh- 
renberg, Darwin, and Jukes. The opportunities for investigation which the Expedition 
afforded were of the most extended kind, and enabled us to make personal examinations 
