123 
a Theory oj the Earth . 
whereas if he has a collection of memorandums on which 
he can from time to time cast his eye, he will be remind- 
ed of all those objects which ought to engage his atten- 
tion. This collection, confined at first, will be extended 
and improved in proportion as he acquires ideas, and 
may furnish hints to travellers who, without being vers- 
ed in geology, wish to collect, in the countries they vi- 
sit, observations that may be useful to those who study 
that science.* 
Agreeably to these principles, I have always prepared 
for all my journeys a list of those objects, for examining 
which that journey was intended. I propose here, how- 
ever, a more extensive plan. I wish to direct the tra- 
# veller, and even the sedentary philosopher, in all the re- 
searches w hich ought to engage their attention, if they 
are desirous of contributing towards the progress of a 
theory of our globe. I do not flatter myself that I shall 
be able to give a complete view of every thing that re- 
mains to be done : what I offer will be only an imperfect 
sketch, but this sketch will be at least useful till some 
one produce a better. Several of the observations and 
questions which I here propose as problematic, seem in- 
deed to have been already resolved ; but as most solu- 
tions of this kind are founded merely on analogy, the 
contrary of which is always physically possible, it is 
proper, in my opinion, to keep the eyes of naturalists al- 
ways open to the grand facts which may be interesting 
to a theory so difficult and of so much importance. 
CHAP. i. 
Astronomical Principles . 
1. A general system of cosmology, in what regards 
the earth considered as a planet. 
* Voyage dans les Alpes, vol. 1. Preliminary Discourse, 
