114 ILLINOIS BIOLOGICAL MONOGRAPHS [212 
EXPLANATION OF PLATE 
Fic. 19. Rock bed of Big Vermilion River one mile below Middle Fork. Station 30. 
October 8, 1920. 
Fic. 20. Sandbar in center of riverbed, several hundred feet below fig. 1. Station 30. 
October 8, 1920. 
Fic. 21. Junction of Boneyard with Salt Fork. Boneyard on right above ice. December 
20, 1919. 
