third editions of my Introduction to Geology and both editions of my 

 History of Land Mammals in the Western Hemisphere were made by 

 him. Mr. Horsfall accompanied me in the tour of the museums in the 

 spring and summer of 1934. We began with the Carnegie Museum in 

 Pittsburgh, then went to the Field Museum in Chicago, the Morrill 

 Museum of the University of Nebraska at Lincoln, Neb., the Colorado 

 Museum of Natural History at Denver, the museum of the State School 

 of Mines, at Rapid City, S.D. In the autumn, we resumed our travels 

 and visited the museums at Amherst College, Yale and Harvard Uni- 

 versities, and the National Museum at Washington. To the American 

 Museum of Natural History in New York we made daily visits for many 

 weeks and, of course, we had a great deal of work to do in our own 

 museum at Princeton, which contains one of the largest and finest of 

 the many White River collections, thanks to the brilliant work of 

 Hatcher and Sinclair. 



The immense enterprise was too much for my unassisted strength 

 and so my former pupil and present colleague. Professor G. L. Jepsen, 

 has collaborated with me in the preparation of parts of the monograph 

 and another one-time pupil. Dr. Albert E. Wood, has written Parts II 

 and III on the rodents and rabbits of the White River fauna. Sinclair 

 always maintained that we didn't know what a task we had undertaken 

 and that we were "biting off more than we could chew." By relieving us 

 of work for which we were not well fitted. Wood has made possible the 

 completion of the magnum opus, the end of which is now (April 1939) 

 in sight. 



Another large undertaking was a new edition of my Land Mammals, 

 which the publishers declined to assume, because of the uncertainties in 

 business prospects. Once more, the Philosophical Society came to my aid 

 and appropriated $7,000 to finance the work, which had to be rewritten 

 completely, for in the twenty-five years that had passed since the publica- 

 tion of the first edition such an immense body of new discovery and 

 material, in both North and South America, had been accumulated that 

 the old book was entirely out of date and could not be patched. The 

 Society's liberality gave me an opportunity to reillustrate the book on an 

 adequate scale; the new edition has 420 figures, two-thirds of them new 

 and mostly Mr. Horsfall's work. The two projects, the monograph and 

 the new edition (really a new book) have been mutually helpful and, to 

 both, our pilgrimage among the museums has been an indispensable 

 preliminary, for only in this manner could much of the finest material 



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