466 REVIEWS 



the effects of snow banks. The thickness of the neve fields which did 

 not become glaciers is estimated to have been loo to 150 feet, and the 

 conclusion is reached that, on a grade of about 12 per cent., the neve 

 must attain the thickness of at least 125 feet in order to have motion. 

 Certain phases of the problem of glacial motion are touched, and 

 the conclusion reached that the cause of glacial motion is to be sought 

 in the weight of the ice mass, and that it is independent of the tem- 

 perature of the air. No attempt is made, however, to decide the real 

 nature of glacial motion, or what processes are involved in it. 



R. D. S. 



Animal Report of tlie Board of Regents of the SmitJisonian Institntion, 

 showing the Operations, Expenditures, and Condition of 

 the Institution for the year ending June 30, 1899. 



In the appendix accompanying the official report of the governing 

 bodies and the secretary -of the Smithsonian Institution, a complemen- 

 tary number of geological articles are introduced. These are, for the 

 most part, republications, and include "On Lord Kelvin's Address on 

 the Age of the Earth as an Abode Fitted for Life," by T. C. Chamber- 

 lin ; "An Estimate of the Geological Age of the Earth," by J. Joly; 

 " The Petrified Forests of Arizona," by Lester F. Ward ; " Present 

 Conditions of the Floor of the Ocean ; Evolution of the Continental 

 and Oceanic Areas," by Sir John Murray; "The Truth About the 

 Mammoth," by Frederic A. Lucas ; " Mammoth Ivory," by R. Lydek- 

 ker ; and " Review of the Evidence Relating to Auriferous Gravel Man 

 in California," by William H. Holmes. Several of the physical and 

 biological articles, and those relating to general aspects of science, 

 also possess points of interest to geologists. . C. 



