Mo Gee — Southern Extension of Appomattox Formation. 37 



represent intelligibly the facts and their relations, and the 

 desire for a more comprehensive taxonomy was indicated by 

 semi-arbitrary division of the science into departments defined 

 by community of agencies (physical geology, structural geol- 

 ogy, historical geology, etc.), within which the minor classes 

 were variously defined and grouped. Still later, not only the 

 primary but the secondary categories of phenomena came to be 

 commonly defined by genesis ; and to-day the taxonomy 

 adopted by leading American geologists is predominantly 

 genetic, and geologic research is considered incomplete if it 

 fails to indicate the origin and course of development of the 

 phenomena studied. 



The interrelation of geologic processes is illustrated in ter- 

 restrial gradation — the matter degraded from one spot or region 

 is deposited in some other spot or region ; and commonly, the 

 regions of degradation and deposition are contiguous. It is 

 also illustrated in the deformation of the terrestrial crust, 

 whether antecedent or consequent* — when one part of the ter- 

 restrial crust is heaved another part is thrown ; and commonly 

 the heaved and thrown parts are contiguous. It is illustrated 

 moreover in the relations between deformation and gradation — 

 when a mountain range or a continent is lifted it is attacked by 

 degradation, and when a sea bottom is formed it is subjected 

 to deposition ; and when degradation lightens the continent or 

 mountain it is still further lifted, and when deposition loads 

 the sea bottom it is still further depressed. This interrelation 

 runs through the entire range of geologic processes. It follows 

 that any process operating in one part of a geologic province 

 must be represented by a similar or kindred process in other 

 parts of the same province — i. e., in a mountain province the 

 degradation of one part is represented by degradation (perhaps 

 at different rates) in all parts ; and in a sea province depo- 

 sition in one part is represented by deposition (varying in rate 

 and quality with local conditions) in all other parts. It equally 

 follows that the products of the processes are genetically re- 

 lated — that the sculptured forms produced by degradation are 

 of common genesis and greater or less similarity in form ac- 

 cording to the local conditions, and that the deposited beds are 

 of common genesis and greater or less similarity in volume 

 and material according to the local conditions. It further fol- 



* The various mass movements concerned in the development of continents 

 and mountains are conveniently grouped as deformation, and the various classes 

 of particle movements concerned in the transfer of materials upon the surface by 

 air, water, ice, and other agencies are conveniently grouped as gradation ; the 

 earth movements concerned in the elevation and exposure to degradation of con- 

 tinents are conveniently classed as antecedent; and the earth movements resulting 

 from transfer of materials through the processes of gradation are conveniently 

 classed as consequent. — Cf., Nat. Geog. Mag., vol. i, 1888, pp. 27-36; G-eol. Mag. 

 Decade III, vol. in, 1888, pp. 489-495. 



