Hays, Samuel P. <br/><br/>
Conservation and the gospel of efficiency :  the progressive conservation movement, 1890-1920. 
/ by Samuel P. Hays. 
 - Cambridge :   Harvard University Press,   1959. 
 - 297 p. ;  21 cm. 
 - Harvard historical monographs.  40 .
<br/><br/><label>ISBN: </label>0674165012 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Conservation of natural resources --United States --History; Environmental policy --United States --History.
<br/><br/><label>Dewey Class. No.: </label>333.720973 HAY  / 1596