!has D. Walcott, 



U. S. Geol. Survey. 



jy& 



VOL. VI. JULY, 1898. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors GEO. L. GOODALE, JOHN TROWBRIDGE, 

 H. P. BOWDITCH and W. G. FARLOW, of Cambridge, 



Professors O. C. MARSH, A. E. VERHILL and H. S. 

 WILLIAMS, of New Haven, 



Professor GEORGE F. BARKER, of Philadelphia, 

 Professor H. A. ROWLAND, of Baltimore, 

 Mr. J. S. DILLER, of Washington. 



FOURTH SERIES. 



VOL. VI— [WHOLE NUMBER, CLVL] 



No. 31.— JULY, 1898. 



WITH PLATE I. 



NEW HAVEN, CONNECTICUT. 



1898. 



TUTTLE, MOREHOUSE & TAYLOR, PRINTERS, 125 TEMPLE STREET. 



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

 foreign subscribers of countries in the Postal Union. Remittances should 

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