CHAPTER VIII.

CHRONOLOGICAL CLASSIFICATION OF ROCKS.

Aqueous, plutonic, volcanic, and metamorphic rocks, considered chronologically--Lehman's division into primitive and secondary--Werner's addition of a transition class--Neptunian theory--Hutton on igneous origin of granite--How the name of primary was still retained for granite--The term "transition," why faulty--The adherence to the old chronological nomenclature retarded the progress of geology--New hypothesis invented to reconcile the igneous origin of granite to the notion of its high antiquity--Explanation of the chronological nomenclature adopted in this work, so far as regards primary, secondary, and tertiary periods 89