VOL. XL. SEPTEMBER, 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. DAVIS, of Cambridge, 



Professors ADDISON E. VEBEILL, HOEACE L. WELLS, 



LOUIS V. PIESSON, HEEBEET E. GEEGOET 



and HOEACE S. TTHLEB, of New Haven, 



Professor HENRY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. J. S. DILLEE, of Washington. 



FOURTH SERIES 



VOL. XL— [WHOLE NUMBER, CXCJ. 

 No. 237— SEPTEMBER, 1915. 



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NEW HAVEN, CONNECTICUT. 



1915. 



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