UNITED 

 STATES 

 MINERAL 

 RESOURCES 



DONALD A. BROBST and WALDEN P. PRATT, Editors 



GEOLOGICAL SURVEY PROFESSIONAL PAPER 820 



■| "0 "H 'M 

 •SSVW '310H SGOOM 



AdVyGH 



AyoiVHoavi 

 T-yQiooioia 



UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON-. 1973 



/ 



t 



