282 REVIEWS 



The systematic treatment of crystallography which the author pub- 

 lished several years ago is not incorporated in the Mineralogy. The 

 treatment and the lists of occurrences appear to be comprehensive. 

 As in most textbooks in mineralogy, the references to sources of infor- 

 mation relating to occurrences are inadequate. Such references, 

 although adding greatly to its bulk, would vastly increase the useful- 

 ness of a textbook on mineralogy. A valuable feature is a group of 

 tables listing separately the minerals containing each element. 



W. H. E. 



The Pleistocene Deposits in Warren County, Iowa. By John 

 Littlefield Tilton. Chicago: The University of Chicago 

 Press, 191 1. Pp. 42; figs. 7. 



As Warren County lies just south of Des Moines beyond the reach 

 of the later ice invasions, the chief Pleistocene features of this region 

 are the sub-Aftonian and Kansan till sheets, the interglacial Aftonian 

 sands and gravels, and the post-Kansan loessial and other deposits. 

 The most serious problem is found in differentiating the sub-Aftonian 

 and Kansan tills, especially since the intervening Aftonian horizon- 

 marker sometimes becomes so scant or obscure as to afford little help 

 in separating the two tills. Though both till sheets were deposited by 

 •glaciers from the Keewatin gathering-ground, certain minor differences 

 are cited by the author as distinguishing them. Large pebbles and 

 bowlders are said to be more common in the Kansan than in the sub- 

 Aftonian in the region under study. Among the stony constituents 

 the author notes red quartzite as characteristic of the Kansan but not 

 of the Aftonian and sub-Aftonian, a view supported by a series of pebble 

 classifications made in the typical Aftonian region by the reviewer. 



The author assigns much greater thickness to the sub-Aftonian than 

 to the Kansan in the region under study and attributes much of the 

 present topography to drainage lines cut in this older drift during the 

 Aftonian interglacial period, believing that, while the later Kansan 

 invasion has partially masked this Aftonian topography by concealing 

 some of the minor valleys, it has not obliterated the larger ones. 



R. T. C. 



