ECOLOGICAL STUDY OF DRY RUN 113 



type of bottom found and, as will be shown, accounts in part for 

 the disappearance of the stream in the lower part of its course. 

 No little interest was attached to this phase of the study, as it 

 was believed that it had a bearing on a serious epidemic con- 

 nected with the water supply of Cedar Falls. 



From the source to the junction of the two branches, the west 

 branch may be conveniently divided into five units, figure 11. 1. The 

 marshy area represented in the map above Station 1. 2. The spring 

 and pool area extending from Station 1 to Station 4. 3. The slow- 

 flowing mud-bottomed area extending from Station 4 to the mouth 

 of a small tributary at the north end of "The Diagonal Road." 

 4. The gravel, mud and limestone-bottomed area extending from the 

 end of the "diagonal" to the quarry, at 10. 5. The limestone area 

 extending from the quarry to the "springs" two miles away. 



The work of making the survey extended over two years. With 

 the assistance of two of the author's students, Mr. Victor Peterson 

 and Mr. George Hendrickson, the course of the stream was care- 

 fully surveyed. At, regular intervals measurements of the depth and 

 width were made and any exceptional variations recorded. From 

 the figures, the graphs for the course and^ depth and width were com- 

 piled. The figures given for depth and width are those found when 

 the stream is at its very lowest during protracted periods of dry 

 weather. It is planned that in a subsequent article the figures for 

 the stream in time of flood will be given. The depth between sta- 

 tions 6 and 9 is so variable, due to showers, that no attempt was 

 made to standardize it. Each photograph is taken looking towards 

 the stream from the place indicated by the corresponding figures 

 on the map. 



The west branch of Dry Run rises in a marshy area southwest 

 of the rural school shown in the map. This area extends to Station 

 1 on the map and in it the water scarcely flows. Dense growths of 

 sedges practically hide the course of the stream. The bottom is a 

 soft black mud and in the summer during dry weather this area 

 appears only as a region of wet mud. No fishes were found in this 

 area in spite of the fact that wherever there was a little water this 

 was seined with a scoop net. 



The region from Station 1 to Station 4 is interesting because 

 there is always much more water here than one would expect to find 

 from a study of the lower stretches of the stream. Beginning just 

 above the clump of willows shown in figure 12 a series of springs 

 appears in the bed of the stream. The uppermost of these are shalr 



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