Wilmington Inr/W-e Free Library 
Wilmington, Delaware 
THE 
STRUCTURE AND DISTRIBUTION 
Off 
GOEAL-EEEFS. 
INTRODUCTION. 
The object of this volume is to describe from my own 
observation and the works of others, the principal 
kinds of coral-reefs, and to explain the origin of their 
peculiar forms. I shall not here treat of the poly- 
pifers, which construct these vast works, except as 
to their distribution, and the conditions favourable 
to their vigorous growth. 
Without any distinct intention to classify coral- 
reefs, most voyagers have spoken of them under the 
following heads : 4 lagoon-islands ’ or £ atolls,’ ‘ barrier ’ 
or * encircling reefs,’ and ‘ fringing ’ or ‘ shore reefs.’ 
The lagoon-islands have received much the most atten- 
tion ; and it is not surprising, for everyone must be 
struck with astonishment, when he first beholds one of 
