124 Gregory — Progress in Interpretation of Land Forms. 



region. Where the streams sink away, or where the lakes which 

 receive them have dried up, the finer products of the erosion 

 of a large territory are left to be removed in dust storms. 



II. The second . . . source is the residuary products of a 

 secular disintegration. ' ' 



The evidence presented by Pumpelly for the eolian 

 origin of loess — structure, texture, composition, fossil 

 content and topographic position — is complete, and to him 

 belongs the credit for the correct interpretation of the 

 Mississippi valley deposits. Unfortunately his contribu- 

 tion came at a time when the geologists of the central 

 States were intent on tracing the paths and explaining 

 the work of Pleistocene glaciers, and the belief was 

 strong that loess was some phase of glacial work. Its 

 position at the border of the Iowan drift so obviously 

 suggests a genetic relation that the fossil evidence of 

 steppe climate suggested by Binney in 1848 65 was mini- 

 mized. Students of Pleistocene geology in Minnesota, 

 Iowa, Nebraska, Missouri, although less vigorous in 

 expression, were substantially in agreement with Hilgard 

 (1879). 66 "The sum total of anomalous conditions 

 required to sustain the eolian hypothesis partakes 

 strongly of the marvellous." The last edition of Dana's 

 Manual, 1894, and of LeConte's Geology, 1896, the two 

 most widely used text books of their time, oppose the 

 eolian theory, and Chamberlin, in 1897, 67 states: "the 

 aqueous hypothesis seems best supported so far as con- 

 cerns the deposits of the Mississippi Valley and western 

 Europe" (p. 795). Shimek, in papers published since 

 1896 has shown that aquatic and glacial conditions can 

 not account for the loess fossils, and the return to the 

 views of Pumpelly that the loess was deposited on land 

 by the agency of wind in a region of steppe vegetation is 

 now all but universal. 



Glacial Sculpture. 



Within the present generation sculpture by glaciers has 

 received much attention and has involved a reconsidera- 

 tion of the ability of ice to erode which in turn involves 

 a crystallization of views of the mechanics of moving ice. 

 The evidence for glacier erosion has remained largely 

 physiographic and rests on a study of land forms. ^ In 

 fact, the inadequacy of structural features or of river 



