_iurary, *u. o. ndi. iviu»c» 



~j 



YOL. XLI. 



MAECH, 1916. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors GEOEGE L. GOODALE, JOHN TROWBBIDGE, 

 W. G. FAELOW and WM. M. DAVIS, op Cambridge, 



Professors ADDISON E. VEBEILL, HOEACE L. WELLS, 



LOUIS V. PIESSON, HEEBEET E. GEEGOEY 



and HOEACE S. UHLEE, of New Haven, 



Professor HENEY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. J. S. DILLER, of Washington. 



FOURTH SERIES 



VOL. XLI— [WHOLE NUMBER, CXCIJ. 

 No. 243— MARCH, 1916. 



NEW HAVEN, CONNECTICUT. 



1916. 



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



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

 Postal Union ; $6,25 to Canada. Eeniittances should be made either by money orders, 

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