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VOL. L ' AUGUST, 1920 



Established by BENJAMIN SILLIMAN in 1818. 



THE ij& 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors GEOEGE L. GOOD ALE, JOHN TROWBRIDGE, 

 and WM. M. DAYIS, of Cambridge, 



Professors A. E. VERRILL, HORACE L. WELLS, CHARLES 



SCHUCHERT, H. E. GREGORY, and HORACE S. 



UHLER, of New Haven, 



Professor JOSEPH S. AMES, of Baltimore, 

 Mr. J. S. DILLER, of Washing 



FOURTH SE 

 VOL. L— [WHOLE NU 



No. 296— AUGUST, 1920 



WITH PLATE I. 



NEW HAVEN, CONNECTICUT. 



19 20. 



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