&P&-73 ^JJL 



THE 



AMERICAN 



JOURNAL OP SCIENCE. 



Editor: EDWARD S. DANA. 



ASSOCIATE EDITOES 



Professors GEORGE L. GOODALE, JOHN TROWBRIDGE, 

 W. G. FARLOW and WM. M. DAVIS, of Cambridge, 



Professors ADDISON E. VERRILL, HORACE L. WELLS, 

 L. V. PIRSSON and H. E. GREGORY, of New Haven, 



Professor HENRY S. WILLIAMS, of Ithaca, 

 Professor JOSEPH S. AMES, of Baltimore, 

 Mr. J. S. DILLER, of Washington. 



FOURTH SERIES 



VOL. XXXI— [WHOLE NCFMBEE, CLXXXL] 



WITH FOUR PLATES. 



NEW HAVEN, CONNECTICUT. 



1911. 



JlfrlOt 



