CHAPTER VIII.

STRATIFIED ROCKS OF ORGANIC ORIGIN--ILLUSTRATIONS FROM ANIMAL LIFE.

Nature of Organic Rocks--Carbonate of Lime extracted from the Sea by the Intervention of minute Animalcules--Chalk Rock--its vast Extent--supposed to be of Organic Origin--A Stratum of the same kind now growing up on the Floor of the Atlantic Ocean--Coral Reefs and Islands--their general Appearance--their Geographical Distribution--their Organic Origin--Structure of the Zoophyte--Various Illustrations--Agency of the Zoophyte in the Construction of Coral Rock--How the sunken Reef is converted into an Island--and peopled with Plants and Animals--Difficulty proposed and considered--Hypothesis of Mr. Darwin--Coral Limestone in the solid Crust of the Earth, 118