Chas. D. Walcott, 



U. S. Geological Survey. 



YOL. XL. DECEMBER, 1890. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



EDITOES 



JAMES D. and EDWARD S. DANA. 



ASSOCIATE EDITOES 



Professors JOSIAH P. COOKE, GEORGE L. GOODALE 

 and JOHN TROWBRIDGE, of Cambridge. 



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



New Haven, 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



YOL. XL.— [WHOLE NUMBER, CXL.] 

 No. 240.— DECEMBER, 1890. 



WITH A MAP, PLATE X. 



NEW HA YEN, CONN. : J. D. & E. S. DANA. 



1890. 



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



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