VOL. L DECEMBER, 1920 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors GEORGE L. GOODALE, JOHN TROWBRIDGE, 

 and WM. M. DAVIS, of Cambridge, 



Professors A. E. VERRILL, HORACE L. WELLS, CHARLES 



SCHUCHERT, H. E. GREGORY, and HORACE S. 



UHLER, op New Haven, 



Professor JOSEPH S. AMES, of Baltimore, 

 Mr. J. S. DILLER, of Washington. 



FOURTH SERIES 

 VOL. L— [WHOLE N UMB^lg, qfgjft 



No. 300— DECEMBfe^giag^u^^ 



NEW HAVEN, CONNECTICUT. 



19 20. 



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