568 REVIEWS 



advanced classes, but though his pupils were not numerous, they were 

 picked men, and the list of those who were trained under him includes not 

 a few of the leading geologists of the country today. 



The story is chiefly told by his letters to his favorite brother, William 

 Dwight Whitney — letters which reveal the man without the reserve which 

 usually accompanied hm, and which portray in a very graphic and vivid 

 style much of the history of early geological exploration in this country. 



R. T. C. 



Iowa Geological Survey, Vol. XIX, Annual Report, 1908. With 



Accompanying Papers. Des Moines, 1909. Pp. 806, 22 plates, 



117 figures. 



Coal is the principal topic of this volume. Besides the Seventeenth 



Annual Report of the State Geologist, Professor Samuel Calvin, it contains 



the following papers: "Mineral Production in Iowa in 1908," by S. W. 



Beyer, pp. 1-20; "Coal Deposits of Iowa," by Henry Hinds, pp. 21-396; 



"Fuel Values of Iowa Coals," by F. A. Wilder, with analyses of Iowa coals 



by James H. Lees and A. W. Hixcon, pp. 397-519; "History of Coal 



Mining in Iowa," by James H. Lees, pp. 521-88; "Coal Statistics," 



by S. W. Beyer, pp. 591-97; "General Section of the Des Moines Stage 



of Iowa," by James H. Lees, pp. 598-604; "The Carboniferous Section 



of Southwestern Iowa," by George L. Smith, pp. 605-57; "Bibliography 



of Iowa Coals," compiled by James H. Lees, pp. 659-87; "Peat Deposits 



in Iowa," by S. W. Beyer, pp. 6S9-730; "Bibliography of Iowa Peat," 



compiled by James H. Lees, pp. 731-33; "Flora of Northern Iowa Peat 



Bogs," by L. H. Pammel, pp. 735-77. 



R. T. C. 



Radioactivity and Geology. An Account of the Influence of Radio- 

 active Energy on Terrestrial History. By J. Joly. Pp. 287, 

 pis. 6, figs. 4. New York: Van Nostrand Co., 1909. 

 The discovery of radioactivity has opened the way for quite a new 

 conception of many geologic phenomena. Fresh light has been thrown 

 upon obscure and difficult problems, old explanations have been weakened 

 or displaced, and alternative hypotheses have been framed to explain 

 various phenomena. Radioactivity when first discovered appeared to 

 have its chief interest in the domain of the physicist and the chemist. How 

 vital a role it may yet prove to play as an active geologic agent, how wide 

 a range of geologic processes it may yet be found to enter as a decisive 



