184 CHEMISTRY OF THE EARTH. 



tor ; that is to say, those substances which are exempt from biological 

 laws, but come within the domain of physics and chemistry. Chemical 

 change implies disorganization, and all so-called chemical species are 

 inorganic, that is to say, unorganized, and belong to the mineral king- 

 dom, whose natural history is thus i)hysical and chemical, while that of 

 the vegetable and animal kingdoms is biological.* 



§ 3. It might, at first sight, seem foreign to our present subject to 

 spealc in this connection of the moral, social, and political history of 

 mankind, dependent upon the laws of psychology and sociology. It is, 

 however, to be remarli:ed, that while in the abstract order ea(;li science 

 is independent of that which follows it in the series, it is far diiferent in 

 the concrete sciences. This is seen in the familiar example of the de- 

 l)endence upon each other of the animal, vegetable, and mineral king- 

 doms, and it is evident that man puts in movement agencies which are 

 constantly at work modifying alilce physical geography and the rela- 

 tions of the mineral, vegetable, and animal world to such an extent that 

 human history must not be disregarded in the study of the lower reigns 

 of nature. 



§ 4. From what has gone before it will be evident that under the com- 

 mon term of geology are generally confounded two distinct branches of 

 study ; the first or abstract division being that of the physical, chemical, 

 and biological laws which have presided over the development of the 

 globe, and the second or concrete division, the natural history of the 

 earth as displayed in its physical structure, stratigraphy, mineralogy, 

 l^aleontology. The name of geognosy, employed by some authors, may 

 very appropriately be retained for the latter, while that of geology is 

 restricted to the former division. It is iiroposed in the following pages 

 to consider briefly some of the more important points in the chemical 

 history of the globe ; in doing which it will be necessary to notice also 

 its astronomical and i^hysical history, and the relations of organic life, in 

 so far as they are concerned in the chemical history of the earth in its 

 various stages of development. The scheme thus embraced is so great 

 that in the limits of the present essay nothing more can be attempted 

 than a sketch which shall embrace some of the most striking facts in 

 the history of the forming globe considered as a condensing nebulous 

 mass, in the chemistry of the air, sea, and earth in past ages, and in the 

 relations of the central heat to the superficial portions of the earth, by 

 which we shall endeavor to exi^lain certain tacts in dynamical geology, 

 such as the great movements of the earth's crust and the phenomena of 

 earthquakes and volcanoes. 



.§ 5. The nebular hypothesis, as it is called, which supposes that our 

 solar system and all the worlds of space have come from the condensa- 

 tion of diftused vapors, has received strong confirmation from the dis- 

 coveries made by the spectroscope. We now know that there exist in 

 the heavens nebuhe consisting of luminous gas ; that is to say, vaporous 

 matter shining by its own light, which we may, with great probability, 

 regard as the primal matter out of which, as the elder Herschel sug- 

 gested, suns and planets have been formed by a process of condensation. 

 By the aid of the telescope and the spectroscope we find in the heavens, 

 planets — bodies like our earth, shining only by reflected light; suns, — 

 self-luminous, radiating light from solid matter ; and, moreover, true 

 nebuhe, or masses of luminous vapor. These three forms represent 

 three distinct phases in the condensation of the primeval matter, from 

 which our owu and other planetary systems have been formed. 



* T. S. Huut, oil the Objects and Method of Mineralogy. American Journal of SrJ- 

 euce, [2,1 xliii; 203. • 



