548 REVIEWS 



general conclusions already reached. In the Cedar county report, on 

 the other hand, Mr. Norton places clearly before the reader the facts 

 as, to the structure and situation of the beautiful land forms to which 

 McGee has given the Wdivae. paha, and also states the various hypotheses 

 which have been suggested for their origin. He makes no attempt, 

 however, to balance the probabilities and reach a decision in the 

 matter. The same method is observed in the discussion of the high 

 dips observed in the Gower limestone of the Niagara. This is con- 

 fessedly a difficult problem, and its solution is wisely left until the 

 whole area shall have been studied. 



In the reports on Page and Pottawattamie counties the survey 

 takes up the southwestern portion of the state. Apparently most inter- 

 esting results are likely to follow this survey. Mr. Calvin's suggestion 

 that the drift of Page county may be the pre-Kansan instead of the 

 Kansan fits in with many of the known facts of the field in Iowa and 

 neighboring states. It is a far-reaching suggestion, and the develop- 

 ment of the hypothesis will be watched with interest. In Pottawat- 

 tamie county the facts are possibly susceptible of either interpretation. 

 Mr. Udden does not, however, discuss the probabilities. His report 

 is particularly interesting to the general student in the large use which 

 he makes of mechanical analyses in the study of the drift. This is a 

 method which seems likely to become more and more useful in the study 

 of unconsolidated materials. The important results already reached 

 by Whitney in the study of soils seem merely the forerunners of what 

 is possible on a wider application of the method to the study of geo- 

 logical problems in general. Mr. Udden's hypothesis of the origin of 

 the rivers of the county is ingenious, but the argument is not alto- 

 gether convincing. The suggestion that the surface of a great ice 

 sheet would afford a better opportunity for the development of such a 

 regular system of rivers than the drift surface left by the melting away 

 of the ice seems open to question. The surface of the Kansan drift, 

 it is true, is everywhere notably even. It is impossible, however, to 

 suppose that so thick and widespread a drift sheet as this would be laid 

 down without the development of moraines and other surface irregu- 

 larities. Yet such irregularities, where they now occur, are very faint, 

 and are apparently the marks of much greater original irregularities. 

 The present plane surface seems likely to be a result of erosion itself. 

 Remembering the long period since these older drifts were deposited 

 and the manifestly great erosion to which they have been subjected, it 



