Office Geological Survey. 

 JSTo. 185." Yol. XXXI. MAY, 1886. 



Established by BENJAMIN SItLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



EDITORS 



JAMES D. and EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors ASA GRAY, JOSIAH P. COOKE, and 

 JOHN TROWBRIDGE, of Cambridge, 



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



New Haven, 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



VOL. XXXI. -[WHOLE NUMBER, OXXXI.J 



No. 185— MAY, 1886. 



WITH PLATE IX. 



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

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