142 A CENTURY OF SCIENCE 



were substantially established by the interesting debate 

 in the Journal led by Chamberlin, Wright, Upham and 

 Dana. 61 Contributions since 1895 have been concerned 

 with the degree rather than the fact of complexity, and 

 continued study has resulted in the general recognition 

 of five glacial stages in North America and four in 

 Europe. 



The Loess as a Glacial Deposit. 



A curious side-product of the study of glaciation in 

 North America is the controversy over the origin of loess. 

 The interest aroused is indicated by scores of papers in 

 American periodicals and State reports of the last quar- 

 ter of the 19th century papers which bear the names of 

 prominent geologists. 



The "loess" in the valley of the Ehine had long been 

 known, but the subject assumed prominence by the pub- 

 lication in 1866 of Pumpelly 's Travels in China. 62 Wide- 

 spread deposits 200 to 1,000 feet thick were described as 

 very fine-grained yellowish earth of distinctive structure 

 without stratification but penetrated by innumerable 

 tubes and containing land or fresh-water shells. Pum- 

 pelly considered these deposits lacustrine, a view which 

 found general acceptance though combated by Kingsmill 

 (1871), 63 who argued for marine deposition. Baron Von 

 Richthofen's classic on China, which appeared in 1877, 

 amplifies the observations of Pumpelly and marshals the 

 evidence to support the hypothesis that the loess is wind- 

 laid both on dry land and within ancient salt lakes. The 

 conclusions of Von Richthofen were adopted by Pumpelly 

 whose knowledge of the Chinese deposits, supplemented 

 by studies in Missouri, of which State he was director of 

 the Geological Survey in 1872-73, placed him in position 

 to form a correct judgment. He says : 64 



"Recognizing from personal observation the full identity of 

 character of the loess of northern China, Europe and the Mis- 

 souri Valley, I am obliged to reject my own explanation of the 

 origin of the Chinese deposits, and to believe with Kichthofen 

 that the true loess, wherever it occurs, is a sub-aerial deposit, 

 formed in a dry central region, and that it owes its structure to 

 the formative influence of a steppe vegetation. 



The one weak point of Richthofen's theory is in the evident 



