Chas. D. Walcott, 



U. S. Geological Survey. 



No. 204. Vol. XXXIY. DECEMBEE, 1887. 



Established by BENJAMIN SILLIMAN 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, op Cambridge, 



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

 New Haven, 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



YOL. XXXIY. -[WHOLE NUMBER, CXXXIYJ 

 No. 204— DECEMBER, 1887. 



WITH PLATE X. 



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

 1887. 



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