CONTENTS. 



Number 81. 



Page 

 Aet. XXI. — Relationship of some American and Old World 



Birches ; by M. L. Fernald. (With Plates Y-VI) _ . . 167 



XXII. — Fertile Fronds of Crossotheca and Myriotheca, and 

 on the Spores of other Carboniferous Ferns, from Mazon 

 Creek, Illinois ; by E. H. Sellards. (With Plate YII.) 195 



XXIII. — Validity of Idiophyllum rotundifolium Lesquereux, 

 a Fossil Plant from the Coal Measures at Mazon Creek, 

 Illinois ; by E. H. ISellards 203 



XXIY. — Precipitation of Ammonium Vanadate by Ammo- 

 nium Chloride ; by F. A. Gooch and R. D. Gilbert... 205 



XXV. — Additions to the Alunite-Jarosite Group of Minerals ; 



by W. F. HiLLEBRAXD and S. L. Pexfield _ 211 



XXVI. — Niagara Limestones of Hamilton County, Indiana : 



by E. M. KiXDLE 221 



XXVII. — Velocity and the Structure of the Nucleus ; by C. 



Barus - - - - . . 225 



XXVIII. — Corundum and a Graphitic Essonite from Bark- 



hamsted, Connecticut ; by B. K. Emersox 234 



