566 BAILEY WILLIS 



its characteristics and mode of formation. Volume II of China is 

 the statement of his observations in the northern provinces, together 

 with the systematic treatment of the material according to geological 

 systems and periods. 



Volume III, which was to contain a similar discussion of his 

 observations in the southern provinces, and which would, no doubt, 

 have presented, in a revised form, his views on the systematic ques- 

 tions involved, remains unfinished. Volume IV, "Paleontologie," 

 prepared by the specialists to whom his collections were referred, 

 appeared in 1883. 



Von Richthofen's field-work in China and the principal publica- 

 tion of results fall within the decade 1868-77, contemporaneously 

 with the Fortieth Parallel Survey, and there is much besides the 

 coincidence of period to invite a comparison. Each entered a terra 

 incognita marvelously rich in geological facts, displayed on a grand 

 scale; each reaped a magnificent harvest, and that gathered by 

 von Richthofen's individual efforts is worthy of a place beside that 

 of his American colleagues; and each elaborated some theoretical 

 views, which the science has outgrown. But though modern research 

 may find much to correct in their early labors, it owes its opportunity 

 to these pioneers; it should not forget the conditions under which 

 they worked ; and it should be prepared for the advance which science 

 is making, always ready to say in the words of von Richthofen: "I 

 welcome these corrections." 



There is perhaps no better illustration of von Richthofen's method 

 of attacking a problem than the development of his theory of the 

 loess, of which he has given a full account in his various articles upon 

 the subject. He enumerates the extraordinary conditions of its 

 occurrence in China, which seem to preclude its formation by any of 

 the agencies usually invoked to explain the deposition of sediments, 

 and states that as early as his first journey through Shan-si he con- 

 ceived the hypothesis of deposition by wind under the climatic and 

 geographic conditions of the steppes of central Asia. His later work 

 upon the subject was directed to critical investigation of the regions 

 in which a similar process is now going on, and he was fortified in his 

 view at every step by the close analogy between 'the deposits of the 

 desert basins and those of the loess-covered districts. He did not 



