Chas. D. VTalcott, 



U". S. Geol. Survey. 



YOL. XLIII. MAY, 1892 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



EDITOES 



JAMES D. and EDWAED S. DANA. 



ASSOCIATE EDITORS 



Professors JOSIAH P. COOKE, GEORGE L. GOODALE 

 and JOHN TROWBRIDGE, of Cambridge. 



Proeessoes H. A. NEWTON and A. E. VERRILL, of 

 New Haven, 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 

 YOL. XLIII.— [WHOLE NUMBER, CXLIIL] 

 . No. 257.— MAY, 1892. 



WITH PLATE XIII. 



NEW HAYEN, CONN.: J. D. & E. S. DANA. 

 18 9 2. 



TUTTLE, MOREHOUSE & TAYLOR, PRINTERS, 371 STATE STREET. 



Published monthly. Six dollars per year (postage prepaid). $6.40 to foreign sub- 

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