XII. PAST CLIMATES AND CLIMAXES. 



Interpretation of past vegetations. — ^The cardinal principles in the interpre- 

 tation of the vegetations of the geological past were formulated by Clements 

 in the "Development and Structure of Vegetation" (1904 : 136, 107) : 



"The operation of succession was essentially the same during the geological 

 past that it is to-day: from the nature of their vegetation forms, the record 

 deals largely with the ultimate stages of such successions. It is evident that 

 geological succession is but a larger expression of the same phenomenon, dealing 

 with infinitely greater periods of time, and produced by physical changes of 

 such intensity as to give each geological stage its pecuUar stamp. If, however, 

 the geological record were sufficiently complete, we should find unquestion- 

 ably that these great successions merely represent the stable termini of many 

 series of smaller changes, such as are found everywhere in recent or existing 

 vegetation." 



In short, the development and structure of past vegetation can be under- 

 stood only in consequence of the investigation of existing vegetation. How- 

 ever, while the study of fossil floras has steadily advanced our knowledge of 

 geological floristics, especially in the last decade, the field of ancient vegetations 

 remains completely unexplored. This is a direct outcome of the slow recog- 

 nition of the importance of successional studies, as a result of which we are 

 just coming to appreciate the development of vegetation as a special field 

 of research. 



The work of Lyell in geology and of Darwin in biology has led to the uni- 

 versal acceptance of the dictum that the present is the key to the past. Axio- 

 matic as this now seems, it not only unlocked the past, but, what was of much 

 greater importance, it also led to the fundamental principle that the present is 

 the natural and inevitable outcome of the past. Moreover, it made scientific 

 investigation of the past possible for the first time, by asserting that processes 

 of change are uniform and continuous or recurrent. The appUcation of this 

 axiom to climatology has recently yielded the most promising results (Douglass, 

 1909, 1914; Humphreys, 1913; Huntington, 1914), and there seems to be no 

 question of its imique value in reconstructing the geological succession of 

 climax formations, and the world vegetations formed by them. In this and 

 the following chapters, a consistent attempt is made to apply the fundamental 

 principles of development and structure to the three great vegetations of 

 geological history, and to trace the major and minor successions, with as much 

 detail as the record justifies at this time. In this, the law of recapitulation 

 will be found to play a decisive part, since the ontogeny of each formation, as 

 shown in the prisere, sums up the major phases of its phylogeny, as seen in 

 the eosere and geosere. 



As a matter of convenience, it is proposed to designate the study of past 

 vegetation as paleo-ecology, or pahcology in the contracted form. This field 

 bears the same relation to paleobotany that ecology does to botany proper. 

 It comprises the response of ancient plants and communities to their 

 habitats, as well as the reactions upon the latter, and includes both autecology 

 and synecology as proposed by Schroter (1902 : 63). No sharp line need be 



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