Explanatory Note 



The series embodies results of investigations ^ usually of restricted 

 scope, intended to aid or direct management or utilization practices and 

 as guides for administrative or legislative action. It is issued in limi- 

 ted quantities for the official use of Federal, State or cooperating 

 Agencies and in processed form for economy and to avoid delay in publicationo 



Washington, D«C. 

 July, 1952 



