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 actioHo It is issued in limited quantities Tor the 

 official use of Federal, State or cooperating agencies and in 

 processed form for economy and to avoid delay in publication. 



Washington, Do C< 

 March 1952 



