Library, U. :5. INat. Museum. 



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YOL. XLIY. 



SEFTEMBEE, 191Y. 



Established by BENJAMIN SJILIMAN 



^a?.VAt)t - 5 1917 'i 



THE 



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AMERICAN 



JOURNAL OP SCIENCE 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITOES 



Professors GEORGE L. GOODALE, JOHN TROWBRIDGE, 

 W. G. FARLOW AND WM. M. DAVIS, op Cambridge, 



Professors ADDISON E. VERRILL, HORACE L. WELLS, 



LOUIS V. PIRSSON, HERBERT E. GREGORY 



and HORACE S. UHLER, of New Haven, 



Professor HENRY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, op Baltimore, 



Mr. J. S. DILLER, of Washington. 



FOURTH SERIES 



VOL. XLIY— [WHOLE NtlMBER, CXCIY], 



No. 261— SEPTEMBER, IDTT. 



WITH PLATE I. 



NEW HAVEN, CONNECTICUT. 

 1917. 



THE TUTTLE, MOREHOUSE & TAYLOR CO., PRINTERS, 123 TEMPLE STREET. 



Published monthly. Six dollars per year, in advance. $6.40 to countries in the 

 Postal Union ; $6.25 to Canada. Single numbers 50 cents. 



Entered as second-class matter at the Post OflElce at New Haven, Conn., under the Act 

 of March 3, 1879. 



