VOL. XXXI. 



JANUARY, 1911. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors GEOEGE L. GOODALE, JOHN TROWBRIDGE, 

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



Professors ADDISON E. VERRILL, HORACE L. WELLS, 

 L. V. PIRSSON and H. E. GREGORY, of New Haven, 



Professor HENRY S. WILLIAMS, of Ithaca, 

 Professor JOSEPH S. AMES, of Baltimore, 

 Mr. J. S. DILLER, of Washington. 



FOURTH SERIES 



VOL. XXXI-[W~HOLE NUMBER, CLXXXL] 



No. 181— JANUARY, 1911./^ 



( JAN 



NEW HAVEN, CONNECTICUT. V 



1911. 



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