i6 PRINCIPLES OF STRATIGRAPHY 



raising of the fusing point by increased pressure has led to the as- 

 sumption that, in spite of the great heat, the earth's interior is a solid 

 mass. Dana and Crosby suggested that the earth might be re- 

 garded as a mass of solid iron from the center to within 500 miles 

 of the surface ; others, however, still hold to the fluid theory of the 

 earth's interior, more or less universally accepted at the beginning 

 of the last century, while still others hold to the theory of a gase- 

 ous interior {1:393; 9:58; 10:334; 33) with a zone of liquid mat- 

 ter transitional to the solid crust. 



\T. THE ORGANIC OR BIOSPHERE. This is the sphere 

 of living matter which permeates the atmo- and hydrospheres, and 

 to some extent the upper strata of the lithosphere. Its two main 

 divisions, the plants and the animals, are familiar. The first forms 

 a nearly continuous mantle over the land and the shallower ocean 

 bottoms, and may be spoken of as the phytosphere; while the sec- 

 ond forms a less continuous, though more universally present animal 

 sphere or shell, which may be designated the soosphere. 



INTERACTION OF THE SPHERES. 



Of the known spheres, the lithosphere is the most stable, and the 

 one retaining in a more or less permanent form the impressions re- 

 ceived through the mutual interaction of the spheres upon each 

 other. The cycle of change, as it affects the lithosphere, has been 

 divided (11:12) into: i. Lithogenesis, or the origin and develop- 

 ment of the rocks; 2. Orogenesis, or their deformation (diastro- 

 phism, including epeirogenic elevations), and 3. Glyptogenesis, or 

 the sculpturing of the lithosphere. In lithogenesis all the other 

 spheres participate. Deformation or orogenesis may be referred 

 especially to the influence of the centrosphere and to gravitative 

 forces ; while glyptogenesis is largely accomplished by the at- 

 mosphere and hydrosphere, with minor contributions of the bio- 

 sphere and pyrosphere. 



Sculpturing Processes. 



It will be convenient to treat the sculpturing processes while 

 discussing the characteristics of the spheres most actively engaged 

 therein, leaving the larger aspects of the subject, i. e., the land 

 forms due to sculpture, until we have considered in detail the 

 processes of lithogenesis and orogenesis. 



In its broadest aspects the sculpturing processes may be di- 



