CONTENTS. 



Page 



Art. XIII. — Certain Astronomical Conditions favorable to 



Glaciation ; by G. F. Becker 95 



XIV. — Mineralogical Notes ; by S. L. Penfield. 114 



XV. — Development of the Lungs of Spiders ; by O. L. Sim- 

 mons. (With Plate VIII) 119 



V 



XVI. — Alunite, from Red Mountain, Ouray County, Colo- 

 rado ; by E. B. Hurlburt . . 130 



XVII. — Geographic and Hypsometric Distribution of North 



American Viviparidae ; by R. E. Call. (With Map.). 132 



XVIII. — Mineralogical Notes; by S. L. Penfield and D. 



A. Kreider -. 141 



XIX. — Carboniferous Fossils in the Norfolk County Basin ; 



by J. B. WoODWORTH . 145 



XX. — Determination of Ferrous Iron in Silicates ; by J. H. 



Pratt., j 149 



XXI. — Action of Reducing Agents on Iodic Acid ; by C. F. 



Roberts 151 



XXII. — The Stratigraphic Position of the Thomson Slates; 



by J. E. Spurr 159 



XXIII. — The Generation of Chlorine for Laboratory Pur- 

 poses; by F. A. Gooch and D. A. Kreider 166 



Appendix. — XXIV. — Miocene Artiodactyles from the East- 

 ern Miohippus Beds ; by O. C. Marsh _. 1*75 



SCIENTIFIC INTELLIGENCE. 



Geology and Mineralogy — Geologic Atlas of the U. S., Montana, J. W. Powell, 

 Director, 170. — Relation of double refraction to Soda in Hornblende, A. C. Laxe. 

 172. — New locality for Silurian LimestODe in Northern Michigan, A. E. Sea- 

 man: Etude sur la determination des Feldspaths dans les plaques minces, A. 

 Michel Levy, 173. 



Obittiary — George Huntington Williams, 174. 



