18 SIXTEENTH REPORT. 



PHYSIOGRAPHIC AND MOLLUSCAN SUCCESSION IN LAKE 



POOLS. 



BY H. BURRINGTON BAKER. 

 CONTENTS. 



Introduction. 

 Physiographic Succession. 



A. Types of Lakes. 



B. Types of Lake Pools. 



I. Barrier Beach Tj^pes. 



II. Sand Spit Types. 

 Molluscan Succession. 



A. Molluscs of Douglas Lake. 



B. Molluscs of Lake Lagoons and Pools. 



I. Barrier Beach Types. 



II. Sand Spit Types. 



a. Description of Different Examples. 



b. Comparison of Different Pools. 



III. Temporary Swamps. 



a. Description of Swamps. 



b. Discussion of Swamp Forms. 

 Summary. 



A. Environmental Differences between Lakes, Pools, and Swamps. 



B. Conclusion. 



Keys to Maps and Charts. 

 Bibliography. 



INTRODUCTION. 



The problem under consideration is the physiographic succession in beach 

 pools, which are formed along the shores of larger lakes by wind and current 

 action, and the corresponding ecological succession in the molluscs they 

 contain. Douglas Lake, in Cheboygan County near the northern end of 

 the Southern Peninsula of Michigan, has a number of pools in different 

 stages of formation, and the data given here was mostly collected in that 

 region during the summers of 1911, 1912, and 1913. Less complete studies 

 were also made in Saginaw Bay, off Lake Huron, during the summer of 

 1908(5), and some mention of these pools will also be made in this paper. 



Map 1 is a map of the northern end of the Southern Peninsula of Michigan, 

 showing the situation and the shape of Douglas Lake. The lake was part 

 of the Great Lakes at one of the former glacial lake levels, and has a fauna 

 closely related to the present Lakes Michigan and Huron (6).' 



> The numbers in parentheses refer to the bibliography at the end of the paper. 



