SUBDIVISIONS OF GEOLOGY 21 



4, the form (biomorphology), etc. Structural hydrology comprises 

 the study of composition (hydrochemistry), classification according 

 to form (hydromorphology), such as oceans, lakes, rivers, etc., each 

 of which has developed a special science to v/hich are applied the 

 names oceanography (oceanology, thalassography), the hydrology 

 of oceans ; limnology, the hydrology of the lakes ; and potamology, 

 or the hydrology of the rivers. Structural atmology or meteorology 

 considers the composition of the atmosphere, its density, etc. The 

 composition and structure of the Pyrosphere is only indirectly as- 

 certainable, while those of the Centrosphere fall into the realm of 

 speculation. 



The historic or genetic aspect of these sciences likewise affords 

 an interesting series of parallels. Thus historical or genetic lithol- 

 ogy, or the science of litliogenesis in its broadest sense, deals with 

 the origin not only of the rocks as such, but also of the structures 

 they exhibit, and must necessarily take account of the conditions 

 under which they were formed. The study of the genesis of the 

 stratified rocks is stratigraphy, which, however, is closely bound up 

 with the other branches of the earth science, and cannot be made 

 independent of them. Historical biology or the science of bio- 

 genesis is the science of organic evolution. It may be considered 

 from the botanical side (phylogenesis), or from the zoological side 

 (^oogenesis), with reference to the individual (ontogenesis) or 

 to the race (phylogenesis). Paleontology, or the science of the 

 past life of the earth, traces the phylogeny back through the suc- 

 cessive geologic periods, and is, therefore, the complement of 

 neobiology, or the science of modern life, and further demonstrates 

 the intimate relationship between the organic and the inorganic 

 sciences. Hydrogenesis, atniogenesis, and pyrogenesis are branches 

 of historical geologic science as yet little developed. 



While stratigraphy is thus more especially the science of the 

 genesis of the stratified series of rocks, it necessarily includes and 

 is based upon the study of the rocks themselves, of their arrange- 

 ment or structures, and of the morphology of the earth's surface 

 during their formation. Thus it comprises the subject of Palcc- 

 ogeography, or the geography of former times, and it furthermore 

 takes careful account of the physical conditions of the land and sea 

 as indicated by the organic remains entombed in the strata. Nor 

 can it leave out of consideration the various diastrophic movements 

 and their results, during all the geologic periods ; while igneous 

 activities, in so far as they affected the strata of the earth's crust, 

 also belong to the field of legitimate inquiry for the stratigrapher. 

 In other words, stratigraphy is the science of the evolution of the 



