280 PAST CLIMATES AND CLIMAXES. 



drawn between it and paleobotany, though the latter deals primarily with the 

 structure, evolution, and relationship of fossil species, while palecology sums 

 up all of their environic relations. Ecology comprehends all the complex 

 relations of plants and habitats, but it seems clear that the ecology of existing 

 relations is not only an end in itself, but that it also furnishes all the points 

 of departure which lead to past relations. Hence it appears imdesirable to 

 attempt a rigid distinction between the ecological study of the present and 

 past. But it does serve a useful purpose to have a special term for the field in 

 which the criteria are necessarily all inferential. Futhermore, palecology is 

 characterized by its great perspective, due chiefly to the absence of a large 

 body of facts. This causes the fundamental correlations between the physical 

 world and vegetation on the one hand, and vegetation and the animal world 

 on the other, to stand out in clear relief. As a consequence, palecology is an 

 imspeciaUzed field in which the interrelations of cUmate, topography, vegeta- 

 tion, animals, and man play the paramount r61e. The emphasis in the present 

 treatment will necessarily fall upon the vegetation, because it is both an effect 

 of climate and topography, and a cause in relation to the animal world, and 

 hence serves as the keystone in the whole arch of cause and effect. As a result, 

 palecology is here regarded as comprising the complete sequence of climate, 

 topography, vegetation, and fauna. 



Methods of interpretation. — ^The interpretation of past vegetations rests 

 upon two basic assumptions. The first is that the operation of climatic and 

 topographic forces in molding plant Ufe has been essentially the same through- 

 out the various geological periods. This is a direct corollary of the conclusions 

 of Lyell as to geology, and of Huntington, Humphreys, and others as to clima- 

 tology. The second assumption is the one already quoted, namely, that the 

 operation of succession as the developmental process in vegetation has been 

 essentially uniform throughout the whole course of the geosere. From these 

 two assumptions naturally foUows a third to the effect that the responses of 

 animals and man to climate and to vegetation, both as individuals and in 

 groups, have remained more or less identical throughout geological time. As 

 a consequence of Darwin's work, this has long been accepted for the individual, 

 but as to the community it still awaits detailed confirmation by the new 

 methods of zoecology. Fiuthermore, if all these be accepted as necessary 

 working hypotheses, it is evident that what is true of the parts must be true 

 of the whole plexus of geological causes and biological responses in the past. 



The interaction of physical forces and plant life has already been recognized 

 as complex. This complexity is greatly increased when the relations of animal 

 life are also considered. Through these involved Hfe processes, however, there 

 runs the basic thread of cause and effect which furnishes the clue to the essen- 

 tial relations. This fundamental sequence is (1) habitat, in which climatic and 

 edaphic forces are the direct factors; (2) vegetation; (3) animal communities; 

 (4) human communities. It is clear, however, that the causal relations are 

 not merely hnear and progressive. While vegetation is primarily the result 

 of the action of climate and soil, it is also affected by animals and man in the 

 most striking fashion. At the same time that it exerts a causal effect upon 

 these, it is also reacting in a critical manner upon the habitat itself. Likewise, 

 while vegetation seems the decisive factor in the development and distribution 

 of animal and human communities, physical factors operate directly and 



