GEOLOGY. 



THE science of Geology has for its object the investigation of the 

 structure and history of the earth. Starting from a study and 

 comparison of the operations of the great forces whereby terres- 

 trial changes are produced at the present time, such as the move- 

 ments of the atmosphere, the evaporation, condensation, and 

 precipitation of water, the flow of rivers and glaciers, the distribu- 

 tion of climate, the movements of earthquakes and volcanoes, it 

 inquires likewise into the structure, growth, and geographical dis- 

 tribution of plants and animals. After this preliminary survey of 

 the existing conditions of our planet and its inhabitants, geology 

 proceeds to consider what evidence may be obtainable of changes 

 which have formerly taken place in the inorganic and organic 

 worlds. The materials with which it has to deal in pursuing this 

 investigation are Minerals, Rocks, and Fossils. 



Geological research requires apparatus of a comparatively simple 

 kind. This consists of instruments for the determination of speci- 

 mens, surveying instruments, collections of specimens for analysis 

 ' and comparison, maps and sections to express the results of sur- 

 veying, and to furnish data for the elucidation of the geological 

 structure of different districts. To these may be added diagrams, 

 models, and other illustrations whereby the facts and principles of 

 the science may be made generally known and especially available 

 for the purposes of education. 



MINERALS, considered as part of the materials of geological 



