88 Dr Boue's Geological Observations. 



order to enable us to comprehend more easily the whole details 

 of the complicated structure of the earth's crust. 



III. On the changes that aj)pear to have taken place during 

 the different periods of the JEartJis Jbrmation^ in the cli- 

 mate of our globe, and in the nature, and the physical 

 and geographical distribution of its animals and plants. 



If we attend to the changes produced on the earth by volca- 

 noes, rivers, the ocean, the atmosphere, and various chemical 

 agencies, we shall obtain very simple theoretical ideas, which will 

 enable us to explain the formation of the groups of rocks of 

 which the crust of the earth is composed, by well known physi- 

 cal and chemical facts. The Tabular View of Rocks, given in 

 volume 13th of The Edinburgh Philosophical Journal, shews 

 the causes of the changes that have taken place in the tempera- 

 ture of the surface of the globe, and, in consequence of it, in 

 the three kingdoms of nature ; and it resolves in a very natural 

 manner the greatest geological problem, for it assigns the rea- 

 sons for the formation of the various zones in latitude, longitude, 

 and height, for the establishment of different climates on the 

 earth, for the successive changes in the various creations of the 

 three kingdoms, and for the particular distribution of the re- 

 mains of the ancient or lost creations. All these problems seem 

 to be resolved, by admitting, at a former period, a much greater 

 activity in the chemical actions which are still the source of pre- 

 sently existing volcanoes. This first proposition is founded on 

 a series of facts, stated in my Tabular View of Rocks, from 

 which it appears that the igneous action decreases in a contrary 

 ratio to the Neptunian, from the ancient to the modern periods. 

 If these chemical subterraneous operations have gradually dimi- 

 nished from ancient to modern times, less volcanic matter has 

 been formed, and smaller tracts of countries have been volca- 

 nized or subjected to the igneous action and change ; and as the 

 high temperature of these volcanic products must have elevated 

 the temperature of the atmosphere, it is clear, that, in propor- 

 tion as the formation of these volcanic masses became less con- 

 siderable, the heat of the atmosphere and surface of the earth 

 also diminished. Volcanic actions are generally accompanied by 

 fissures, by fallings in and risings up of tracts of country. These 



