Established by BENJAMIN SHUHAN in 1818. 



THE 



AMEEICAN 



JOURNAL OF SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITOES 



Professors GEOEGE L. GOODALE, JOHN TKOWBREOGE, 

 W. G. FARLOW and WI. M. DAVIS, of 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. 



[-, 



1911 



FOURTH SERIES library 



VOL. XXXI— [WHOLE NUMBER, CLXXXL] 



No. 184— APRIL, 1911. 



NEW HAVEN, CONNECTIC 

 1911. 



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