has D. Walcott, 



U. S. Geol. Survey. 



OL. IY. DECEMBEB, 189T. 



Established by BENJAMIN SILLIMAN in 1818. 

 T II E 



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. YERRILL 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. IY— [WHOLE NUMBER, CLIY.] 



No. 24.— DECEMBER, 1897. 



^VITH PLATE XII. 



NEW HAYEN, CONNECTICUT. 



189T. 



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



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

 scribers of countries in the Postal Union. Remittances should be made either by 

 money orders, registered letters, or bank checks. 



