THE POSTGLACIAL DISPERSAL OF THE NORTH 



AMERICAN BIOTA. 1 



CHAS. C. ADAMS. 

 [From the University Museum, University of Michigan. | 



CONTENTS. 



1. Introduction. 



Recent advances in the accumulation of data and the historic factor in biotic 

 interpretation. 



2. Biotic Preserves During the Ice Age. 



The three waves, their five biotic types, and their postglacial dispersal routes. 



3. Some Factors in Biotic Interpretation. 



The changes of the environment and its correlated successional relation of the 

 biota ; influence of biotic regions upon successional relations ; geographic 

 perspective in habitat study. 



4. Summary and Conclusion. 



5. References. 



i. INTRODUCTION. 



During the last few decades there has been a remarkable ac- 

 cumulation of data on the geographical distribution of the extra- 

 tropical North American biota. In addition to the facts them- 

 selves there has been a great advance in those allied sciences 

 which throw some of the most important side lights upon distri- 

 butional problems the physiographic and geographic histories 

 of definite areas. 



It is of interest to know that the leading factors in this increase 

 in our data have been the surveys by our National Government, 

 especially the work of the U. S. Biological Survey, State Sur- 

 veys and the great activity of our larger museums, although 

 specialists and amateurs must not be overlooked. 



While among many groups there have been notable advances, 

 yet for others our knowledge remains very incomplete, and must 

 apparently remain so because of the immensity of the field and 

 the scarcity of workers. Here even the preliminary organization 

 of data is yet to be made. The recent advance then in distribu- 



1 Read at the Eighth International Geographic Congress, Washington, September 

 9, 1904. 



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