PRINCIPLES 
OF GEOLOGY. 
CHAPTER I. 
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 — Illustrations 
from the history of the progress of Geology of the respective merits of the 
two systems — Habit of indulging conjectures respecting irregular and extra- 
ordinary 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. 
Having considered, in the preceding volumes,, the actual opera- 
tion of the causes of change which affect the earth's surface and 
its inhabitants, we are now about to enter upon a new division 
of our inquiry, and shall therefore offer a few preliminary 
observations, to fix in the reader's mind the connexion between 
two distinct parts of our work, and to explain in what manner 
the plan pursued by us differs from that more usually followed 
by preceding writers on Geology. 
All naturalists, who have carefully examined the arrange- 
ment of the mineral masses composing the earth's crust, and 
who have studied their internal structure and fossil contents, 
have recognized therein the signs of a great succession of former 
changes ; and the causes of these changes have been the object 
of anxious inquiry. As the first theorists possessed but a scanty 
acquaintance with the present economy of the animate and 
inanimate world, and the vicissitudes to which these are sub- 
ject, we find them in the situation of novices, who attempt 
to read a history written in a foreign language, doubting about 
the meaning of the most ordinary terms; disputing, for 
Vol. III. B 
