248 DAVIS— SYSTEMATIC GEOGRAPHY. [Aprils, 



expert ; for in no other way can proper training in the use of types 

 be secured. 



12. Contrasts of Biological and Physiographical Classifications. — 

 It may be worth while to note explicitly that there is little resem- 

 blance between the basis of the physiographic classification of land 

 forms, here outlined, and the phylogenetic classification of organic 

 forms now in vogue. In the latter case resemblance is inherited by 

 actual derivation from common ancestors ; and if similar forms 

 arise as a result of similar environment, independent of relationship 

 by descent, this only serves to emphasize the rule by pointing to 

 the exception from it. In the former case, resemblance is due to 

 repetition of physical conditions, and inheritance naturally has no 

 part to play. Similar structures, acted on by similar processes, at 

 similar rates for similar times will have similar forms ; but as struc- 

 tures, processes, rates and times are all variable, it is not to be ex- 

 pected that identical forms should be developed. All the more 

 need, therefore, of developing a method of rational generalization, 

 whereby the essential features of a landscape may be seized upon as 

 the basis for its description, while the insignificant elements of a 

 landscape may be set aside. It should further be noted that while 

 hybridization is of very limited range among organic forms, there 

 is no limit to it in land forms. All sorts of structures are combined 

 in all sorts of ways and acted on by all sorts of processes at various 

 rates for different periods. This is indeed one of the chief causes 

 of difficulty in physiographical description. Without free crossing 

 of species, the variety of landscape would be much lessened. Phy- 

 siography would then be easier and less interesting than it is now. 



13. Examples of Explanatory Description. — The flood-plain 

 scrolls illustrated in Fig. 1 may be instanced as examples that come 

 very easily under the explanatory description of land forms. It 

 has been ascertained with a high degree of certainty that a winding 

 river, revived to renewed downward corrosion by the uplift of its 

 basin, will increase the radius of curvature of its bends and push 

 every bend down-valley while it is cutting down to grade with re- 

 spect to its new baselevel. If the river had a meandering course 

 when the uplift occurred, the increased width of the meander belt 

 will be shown by the gentle slope of the spurs that enter each 

 meander, as well as by the abrupt bluffs by which each meander is 

 enclosed ; while the down-valley advance of the meander system 

 will be shown by the extension of the enclosing bluff with decreas- 



