m PREFACE. 



Barnes in connection with the geologic functions of life ; and of Professor 

 Julius Stieglitz in connection with chemical subjects. 



The illustrations have been selected from numerous sources, which 

 are usually acknowledged in the text. Especial acknowledgment is 

 due to the U. S. Geological Survey for the use of numerous photographs 

 and maps, and to Mr. G. A. Johnson, who has made many of the draw- 

 ings reproduced in Volume I. The authors are under even larger obli- 

 gations for assistance in the preparation of Volume II, for which acknowl- 

 edgment will be made in the proper place. 



University of Chicago, January, 1904. 



