CONTENTS. 
Vol. III. 
CHAPTER I. 
PAGE 
Connexion between the subjects treated of in the former parts of this work 
and those to be discussed in the present volume — Erroneous assumption of 
the earlier geologists respecting the discordance of the former and actual 
causes of change — Opposite system of inquiry adopted in this work — Illus- 
trations from the history of the progress of Geology of the respective merits 
of the two systems — Habit of indulging conjectures respecting irregular and 
extraordinary agents not yet abandoned — Necessity in the present state of 
science of prefixing to a work on Geology treatises respecting the changes 
now in progress in the animate and inanimate world . . 1 
CHAPTER II. 
Arrangement of the materials composing the earth's crust — The existing 
continents chiefly composed of subaqueous deposits — 'Distinction between 
sedimentary and volcanic rocks — Between primary, secondary, and tertiary — • 
Origin of the primary — Transition formations — Difference between secondary 
and tertiary strata — Discovery of tertiary groups of successive periods — 
Paris basin — London and Hampshire basins — Tertiary strata of Bordeaux, 
Piedmont, Touraine, &c. — -Subapennine beds — English crag — More recent 
deposits of Sicily, &c. ...... 8 
CHAPTER III. 
Different circumstances under which the secondary and tertiary formations 
may have originated — Secondary series formed when the ocean prevailed : 
Tertiary during the conversion of sea into land, and the growth of a continent 
— Origin of interruption in the sequence of formations — The areas where new 
deposits take place are always varying — Causes which occasion this transfer- 
ence of the places of sedimentary deposition — Denudation augments the dis- 
cordance in age of rocks in contact — Unconformability of overlying forma- 
tions — In what manner the shifting of the areas of sedimentary deposition 
may combine with the gradual extinction and introduction of species-to pro- 
duce a series of deposits having distinct mineral and organic characters 23 
c 2 
