VOL. XXXIX. FEBRUARY, 1915. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWAED S. DANA. 



ASSOCIATE EDITORS 



Professors GEOEGE L. GOODALE, JOHN TEOWBEIDGE, 

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



Professors ADDISON E. VEEEILL, HOEACE L. WELLS, 



LOUIS V. PIESSON, HEEBEET E. GEEGOEY 



and HOEACE S. UHLEE, of New Haven, 



Professor HENEY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. J. S. DILLEB, of Washington. 



FOURTH SERIES 



YOL. XXXIX-[WHOLE NUMBER, CLXXXIX]. 

 No. 230— FEBRUARY, 1915. 



WITH PLATE I. 



NEW HAVEN, CONNECTICUT. 

 1915. 



THE TUTTLE, MOREHOUSE & TAYLOR CO., PRINTERS, 123 TEMPLE STREET. 



Published monthly. Six dollars per year, in advance. $6.40 to countries in the 

 Postal Union ; $6.25 to Canada. Keinittances should be made either by money orders, 

 registered letters, or bank checks (preferably on New York banks). 



