GENERAL CONCLUSIONS 471 



grand history of changes in the face of the earth over western 

 North America, by MacGinitie's (2) analysis of climatic trends and 

 fluctuations in this region since Cretaceous time, and by the excellent 

 reviews by Martin (15) and by Blair (17) on the dramatic events of 

 the Pleistocene and their consequences. 



Some new, refined approaches in biogeographical analysis are 

 emphasized. One of these is the quantitative reconstruction of past 

 vertebrate biocoenoses through the study of all identifiable material 

 obtained by soil washing — a truly revolutionary (and long overdue) 

 development, as D. E. Savage (4) indicates. Another major refine- 

 ment is the more precise and penetrating systematic analysis, such as 

 is indicated in most of the reports, notably those by Peabody and 

 J. M. Savage (8), R. R. ^filler (9), and Parkes (16). Another cir- 

 cumstance favoring sound biogeographical conclusions is the life-long 

 devoted specialization on single groups, throughout their range, that 

 is obvious in the contributions by several of the authors, notably 

 A. H. Miller (6), R. R. Miller (9), and the entomologists: Ross (11), 

 Rehn (12), Linsley (13), and Hovanitz (14). Radiocarbon dating 

 becomes a tool of research in blogeography, as in other areas (Mar- 

 tin, 15). Quantitative studies, including pollen analysis, are helping 

 to displace inference with data. And, most effective of all as a lead 

 toward a fuller understanding of the events and processes in bio- 

 geography is the recourse to interdisciplinary and multidisciplinary 

 approaches. 



The fabric of this symposium has been woven of threads that vary 

 so much in color, size, and strength as to make it difficult to pick 

 out these threads to reweave a simple review and conclusion. On 

 some basic lines, however, there is sufficient consensus to permit 

 some generalization. 



One initial thought that seems justified is that blogeography is 

 still a propitious field of inquiry. Certainly, many of the defects of 

 the past are attributable to excessive inference on the basis of Inade- 

 quate data. Through more intensive research, sharpened by new 

 techniques and enriched by Interdisciplinary approach, sound data 

 are certain to result, and broader and more reliable interpretations 

 are bound to develop. Through the symposium there is to be found 

 much justification for this optimism. 



A notable feature of the whole series of papers is that there is 

 hardly a mention of the transoceanic land bridges that blogeog- 



