PRELIMINARY CONSIDERATIONS. 
11 
The knowledge of mankind, therefore, at one age seems but as folly or ignorance in a suc¬ 
ceeding one; and it is the same regarding our own knowledge at different periods. Still 
there are certain principles which never fail, and which man through his whole life, and 
mankind throughout all ages, have acknowledged as fixed and unalterable. It is not the facts 
of observation that change, but the inferences which we draw from them, as our knowledge 
becomes more extended, and facts before unknown are added to the stock. 
Exact knowledge, therefore, consists in those things which can be seen or demonstrated ; 
while in all knowledge of inference, there is progression. Opinions which are often the result 
of imperfect knowledge are liable to change, and the human mind is never advanced by adopt¬ 
ing the opinions of others ; for by that means, man is never made a thinking being, but rests 
upon authority. 
Viewing nature and the mind of man in this light, we are not to look at the imperfections 
in the works of those who preceded us, but to be satisfied to add a few more facts to the great 
store of exact knowledge. We are to consider always that theories and systems are merely 
an exposition of the present amount of knowledge on the subject; and that science is the 
term used by philosophers to designate the conclusions drawn from a systematic arrangement 
of facts, verified by other facts, relating to any portion of nature’s works ; not in the least 
signifying that man’s knowledge is perfect in any department of nature, or that science is less 
susceptible of improvement by the addition of new discoveries. 
In all sciences, the acquisition of new truths exhibits in new light the beautiful operation 
of the laws of nature; and in none more than in geology does it show them operating in a 
uniform and unvarying manner through successive periods, as proved by the organic contents 
of the strata of every geological era. In no science have facts accumulated more rapidly; 
but it is within a comparatively recent period that these have been rightly interpreted, or have 
led to the simple and satisfying, and at the same time stupenduous conclusion, that nature 
has been operating through incalculable periods of time, with the same harmony and unity 
of design as we behold in her present creations. 
The history of geology in our own country, even for a few years past, and within the 
memory of almost every one, shows how rapidly the subject has advanced, till from a word 
scarce comprehended, the application of its principles are of daily adoption among us, and 
the results of its investigations known to all. 
