U. S. Geological Survey. 



VOL. XLL MARCH, 1891, 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



EDITORS 



JAMES D. and EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors JOSIAH P. COOKE, GEORGE L. GOODALE 

 and JOHN TROWBRIDGE, of Cambridge. 



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

 New Hayen, 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



VOL. XLL— [WHOLE NUMBER, CXLL] 

 No. 243.— MARCH, 1891. 



WITH PLATES XI-X1V. 



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

 1891. 



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



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

 scribers of countries in the Postal Union. Remittances should be made either by 

 money orders, registered letters, or bank checks. 



