Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWAKD S. DANA. 



ASSOCIATE EDITORS 



Professors GEOEGE L. GOODALE, JOHN TEOWBRIDGE, 

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



Professors ADDISON E. VEEEILL, HOEACE L. WELLS, 

 L V. PIESSON and H. E. GEEGOEY, of New Haven, 



Professor HENEY S. WILLIAMS, of Ithaca, 

 Professor JOSEPH S. AMES, of Baltimore, 

 Mr. J. S. DILLEE, of Washington. 



FOURTH SERIES 



VOL. XXXI-[WHOLE NUMBEK, CLXXXL] 



No. 183— MARCH, 1911. 



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1911 • * fVonal m>¥ 



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