VOL. XXXI. JUNE, 1911. 



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. 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 — ; — j ; 



Mr. J. S. DILLER, of Washisqv^^S^^ ' nstit 



JUL 5 1 



FOURTH SERIES X^°«al Nto* 



VOL. XXXI-[WHOLE NUMBER, CLXXXL] 

 No. 186— JUNE, 1911. 



WITH PLATE IV. 



-e^Wteonian 



NEW HAVEN, CONNECTICUT*^ L^> 1911 

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