Explanatory Note 



The series embodies results of investigations, usually of 

 restricted soope, intended to aid or direct management or 

 utilization pi^ctices and as guides for adminiatrative or 

 legislative aotion. It is issued in limited quantities for the 

 official use of Federal, State or cooperating agencies and in 

 processed form for economy and to avoid delay in publication. 



Washington, D. C» 

 May 1960 



