Library, U. S. Nat. Museum. 



YOL. XLI. 



FEBRUARY, 1916. 



Established by BENJAMIN SIILIMAN in 1818. 



THE 





AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWAED S. DANA. 



ASSOCIATE EDITORS - 



Professors GEORGE L. GOODALE, JOHN TEOWBEIDGE, 

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



Professors ADDISON E. VEEEILL, HOEACE L. WELLS, 



LOUIS V. PIESSON, HEEBEET E. GEEGOEY 



and HOEACE S. UHLEB, of New Haven, 



Professor HENEY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. J. S. DILLEE, of Washington. 



FOURTH SERIES 



VOL. XLI— [WHOLE NUMBER, CXCIJ. 

 No. 242— FEBRUARY, 1916. 



WITH PLATE III 



NEW HAVEN, CONNECTICUT. 



1916. 



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



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

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