THE PROBLEMS OF GEOLOGY 527 



geology is the science of the physics and chemistry of the earth. It 

 includes mineralogy. These definitions may not be complete, but at 

 least they are true so far as they go. 



It is not necessary, for present purposes, to consider the possible 

 defects of the definitions given, except that for geology. Objections 

 may be raised to defining geology as the science of the physics and 

 chemistry of the earth, on the ground that this definition is inade- 

 quate to cover descriptive and historical geology. It may be said 

 that it is a part of geology to describe the facts exhibited by the earth 

 as they appear, without reference to physics or chemistry. It may 

 be said that the history of events, as shown by the rocks and fossils, 

 does not necessarily require physical or chemical treatment. There 

 is some truth in these statements, but on the other side it may be held 

 that the facts are the results accomplished by physical and chemical 

 work. These facts become important and significant mainly as they 

 are interpreted in physical and chemical terms. The objects of 

 the earth the complex results of chemical and physical work if 

 described without reference to the manner in which the results came 

 about, have comparatively little interest. In reference to historical 

 geology it may be said that this subject gives a chronological arrange- 

 ment of the results of chemical and physical work. 



It thus appears that physics and chemistry are the elementary 

 sciences, while astronomy, biology, and geology may be defined, 

 possibly with some lack of completeness, as the applications of the 

 principles of physics and chemistry to various complex systems. In 

 this sense astronomy, biology, and geology are applied sciences. 



We are now in a position clearly to indicate the relations of geology 

 to the sciences mentioned. So far as the earth is one member of one 

 of the heavenly systems, it is a subject of astronomy. So far as organ- 

 isms constitute a small part of the earth, they are the subject of geo- 

 logy. Since the earth is one of the subjects of astronomy, and since 

 the entire kingdom of organisms constitutes a small part of the 

 material of the earth, geology is closely related on one side to astro- 

 nomy, upon the other side to biology. Geology is one of the children 

 of astronomy. Geology begins with the earth at the time of its astro- 

 nomic birth. As geology is one of the children of astronomy, so biology 

 is one of the children of geology. As the result of various processes 

 upon the earth, chemical and physical, organisms have been formed, 

 and have gone through their long and complex development. But 

 astronomy, geology, and biology grandparent, parent, and child 

 have long existed side by side, and their interaction and mutual 

 effects have been most profound. One cannot be comprehended inde- 

 pendently of the others. 



While geology is very closely related to astronomy and biology, 

 we have seen that it is still more closely related to physics and chemis- 



