Library, U. S. IN at. museum. 

 W VOL. XL. 





DECEMBER, 1915. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE, 



Editor: EDWAKD S. DANA. 



ASSOCIATE EDITORS 



Professors GEOKGE L. GOODALE, JOHN TROWBELDGE, 

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



Professors ADDISON E. VEKEILL, HOEACE L. WELLS, 



LOUIS V. PIESSON, HEEBEET E. GEEGOET 



and HOEACE S. UHLEE, of New Haven, 



Professor HENEY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. J. S. DILLEE, of Washington. 



FOURTH SEEIES 

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