CHEMISTRY OF THE EARTH. 183 



CONTENTS OF SECTIONS. 



1-3, classification of the sciences ; 4, objects of cliomical geology; 5, nebular hypo- 

 thesis; 6, dissociation ; 7, 8, the sun; 9, the cooling earth; lO-l:^, its solidihcation ; 



14, relations of solution to pressure ; 15, on the earth's crust ; 16, 17, probable composi- 

 tion anil relation of earth's crust and atmosphere ; 18, fixation of carbonic acid, its 

 efi'ect on climate ; 19, chemical inlhience of vegetation as a reducing agent ; origin of 

 carbon and sulphurets ; 20, origin of limestones, dolomites, and gypsums ; 21, silicated 

 waters ; 22, relations of potasli and soda ; 23-2G, disintegration of silicated rocks ; 27, 

 their division into two groups ; 28, chemically-formed alnminous and nou-aluminons 

 silicated rocks ; 29, changes in composition of sediments ; 30, 31, metamorphism of 

 rocks ; 32, chemical alteration ; 33, molecular alteration ; 34, porosity of sediments, 

 their aondeusation ; 35, ultimate result of chemical metamorphism ; 36, theory of vol- 

 canic action ; 37, views of Keferstein and Herschel ; 38, the primitive crust ; 39, internal 

 heat ; 40, 41, iuHnence of pressure ; 42, 43, types of igneous rocks ; 44, origin of granites ; 



15, indigenous and exotic rocks ; endogenous rocks or vein-stones ; 46, filling of mineral 

 veins ; 47, source of metals, and theory of metalliferous deposits ; 48, earthquakes ; 49, 

 volcanoes ; 50, 51, their distribution ; 52, causes of subsidence and accumulation of sedi- 

 aients ; theory of mountains ; 53, origin of lavas ; 54, relations of sedimentary deposi- 

 tion to volcanic phenomena ; ancient volcanoes ; 55, modern volcanoes. 



§ 1. In approacliing the study of the chemistry of the earth, or what 

 may be designated chemical geology, it becomes necessary to define the 

 natural objects of that complex study to which is given the general 

 name of geology, and also to consider its connection with the various 

 sciences. To this end, some notions as to the order and the relation of 

 these sciences may not be out of place. Following the classification 

 established by Comte, we distinguish between the abstract sciences, which 

 deal with laws, and the concrete sciences, which have to do with things. 

 In their order the abstract sciences form an ascending series, according 

 to the degree of complexity of their phenomena, " so that each science 

 depends on the truths of all those which precede it, with the addition of 

 peculiar truths of its own." — (J. S. Mill.) At the base of this series are 

 thus placed — 1st, Mathematics^ with its successive divisions of number, 

 geometry and mechanics ; 2d, Abstract Astronomy^ which considers, in 

 addition to these, gravitation, taking coguizjince of number, extension, 

 equilibrium, and motion ; 3d, Physics, comiirehending the laws of weight, 

 cohesion, sound, light, electricity, and magnetism ; ith. Chemistry, which 

 treats of the relations to one auother of the different forms of mineral 

 matter, and their transformations under the physical agencies of light, 

 heat, and electricity ; 5th, Biology, or Physioloyy, to which belongs the 

 study of the laws of organized growth and development ; (3th, Psychology, 

 which considers the laws of mental i^henomena ; and, 7th, Sociology, or 

 the laws of human society, 



§ 2. Parallel with these abstract sciences is a series of concrete or his- 

 torical sciences, dealing not with laws and general principles, but with 

 objects and facts. Of these concrete sciences the first is Descriptive 

 Astronomy, which is the natural history of the planetary and stellar 

 worlds, treating of their movements, dimensions, and cosmical relations. 

 Coming, in the next place, to the history of our own planet, the study of the 

 accidents of its surface and its interior gives rise to Physical Geography 

 and to Structural and Dynamical Geognosy ; whila the bodies which it 

 presents to us are naturally divided into two great classes, the inorganic 

 or mineral kingdom, and the organic, including the vegetable and ani- 

 mal kingdom. The study of these two classes gives rise to two great 

 branches of natural history. Mineralogy and Organography, the latter 

 inchuling Botany and Zoology. The concrete science of mineralogy has 

 for its subject the natural history of all the forms of unorganized mat- 



