CONTENTS. 



Numlber 201. 



Page 



Art. XXI. — Ionization by Collision in Gases and Vapors ; 



by W. A. Barss 229 



XXII. — Geology of Arisaig-Antigonish District, Nova 



Scotia; by M. Y. Williams 242 



XXIII. — Jackson on the Phylogeny of the Echini ; A 



synopsis by C. Schuchert 251 



XXIV.— The Belt and Pelona Series ; by O. H. Hershey . . 263 



XXV. — Absorption and Thickness of thin Films ; by C. C. 



Hutchins 2*74 



XXVI. — The Mazon Creek, Illinois, Shales and their Amphib- 

 ian Fauna ; by R. L. Moodie 277 



XXVII. — An American Jurassic Frog; by R. L. Moodie 286 



XXVIII.— On the Hydrolysis of Metallic Alkyl Sulphates ; 



by G. A. Linhart 289 



XXIX. — On the Hydrolysis of Esters of Substituted Aliphatic 



Acids ; by W. A. Drushel and E. W. Dean 293 



XXX. — An Electromagnetic Effect ; by S. R. Williams... 297 



SCIENTIFIC INTELLIGENCE. 



Physics — Growth of Air Bubbles at the Walls of a Beaker containing a 

 Liquid, when the Gas at the free Surface is not air, C. Baeus, 304. 



Geology and Mineralogy — First Annual Report of the Director of the Bureau 

 of Mines, J. A. Holmes, 305. — Platinum and Platiniferous Deposits of the 

 Ural, L. Dupaec : Gabbros and Associated Bock at Preston, Connecticut, 

 G. F. Loughlin, 306. — Dana's Manual of Mineralogy ; for the Student of 

 Elementary Mineralogy, the Mining Engineer, the Geologist, the Prospec- 

 tor, the Collector, etc., W. E. Ford, 307. 



Miscellaneous Scientific Intelligence — On a Period of 33 "33 in the Earth's 

 Climate, and its connection with Sun Spots, J. Zilius : The Elements of 

 Statistical Method, W. I. King : Archiv fur Zellforschung, 308. 



