IV BULLETIN 184, UNITED STATES NATIONAL MUSEUM 



tory, Prof. Charles Palaclie, of Harvard University, and Dr. H. H. 

 Nininger, of Denver, for the loan of specimens; to Dr. Robert F. 

 Melil, of the Carnegie Institute of Technology, who kindly read the 

 manuscript and made valuable suggestions; and to Prof. Clair 

 Upthegrove, of the University of Michigan, for the use of the facil- 

 ities of the metallographic laboratory of the university. 



Stuart H. Perry. 

 Adrian, Mich., Decemher 1, 1942. 



