INTRODUCTION. 11 



farther off than Neptune. Thus it appears that the earth is a very small 

 object in the universe. Hence we naturally conclude that it is a dependent 

 part of the solar system; that, as a satellite of the suu, in conjunction with 

 other planets, it could no more have existed before the sun, or our planetary 

 system before the universe of which it is a part, than the hand before the 

 body which it obediently attends. 



Although thus diminutive, the laws of the earth are the laws of the 

 universe. One of the fundamental laws of matter is gravitation; and this 

 we trace not only through our planetary system, but among the fixed stars, 

 and thus knoio that one law pervades the universe. 



The rays of light which come in from the remote limits of space are 

 a visible declaration of unity; for this light depends on molecular vibra- 

 tions, — that is, the ultimate constitution and mode of action of matter ; and, 

 by the identity of its principles or laws, whatever its source, it proves the 

 essential identity of the molecules of matter. 



Meteoric stones are specimens of celestial bodies occasionally reaching 

 us from the heavens. They exemplify the same chemical and crystal- 

 lographic laws as the rocks of the earth, and have afforded no new element 

 or principle of any kind. 



The moon presents to the telescope a surface covered with the craters of 

 volcanoes, having forms that are well illustrated by some of the earth's 

 volcanoes, although of immense size. The principles exemplified on the 

 earth are but repeated in her satellite. 



Thus, from gravitation, light, meteorites, and the earth's satellite, we 

 learn that there is oneness of law through space. The elements may differ 

 in different systems, but it is a difference such as exists among known 

 elements, and even if exemplifying new laws, such laws cannot be at 

 variance with those illustrated by nature within reach of terrestrial investi- 

 gation. The universe, if open throughout to our explorations, would vastly 

 expand our knowledge, and science might have a more beautiful superstruc- 

 ture, but its basement-laws would be the same. A treatise on Celestial 

 Mechanics printed in our printing-offices would serve for the universe. 



The earth, therefore, although but an atom in immensity, is immensity 

 itself in its revelations of truth; and science, though gathered from one 

 small sphere, is the deciphered law of all spheres. 



It is well to have the mind deeply imbued with this thought, before 

 entering upon the study of the earth. It gives grandeur to science and 

 dignity to man, and will help the geologist to apprehend the loftier charac- 

 teristics of the last of the geological ages. 



Special aim of geology, and method of geological reasoning. — Geology is 

 sometimes defined as the science of the structure of the earth. But the 

 ideas of structure and origin of structure are inseparably connected, and in 

 all geological investigations they go together. Geology had its very begin- 

 ning and essence in the idea that rocks were made through secondary 

 causes ; and its great aim has ever been to study structure in order to com- 



