Chas. D. Walcott, 



U. S. Geol. Survey. 

 VOL. XLIII. APRIL, 1892. 



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. GOOD ALE 

 and JOHN TROWBRIDGE, of Cambridge. 



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



New Haven, 



. Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



YOL. XLIII.— [WHOLE NUMBER, CXLIIL] 



No. 256.— APRIL, 1892. 



WITH PLATE XII. 



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



18 92. 



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