ECOLOGICAL STUDY OF DRY RUN 



121 



of the stream disappears here. During a normal summer the stream 

 rarely flows beyond these two sink holes. During a wet season or 

 in the spring the stream flows beyond this into the quarry shown in 

 figure 20. Sometimes after a very heavy rain in the summer the 

 water will flow over into this quarry. This is shown in figure 19. 

 Except in time of high spring flood the stream runs its course under- 



FiG. 24. — Limestone ledge seen in Natural Science Park of Iowa State Teachers 

 College. This shows the same layer seen in Figure 23 only higher from the 

 creek bed and illustrates the tilt in the strata of rock contrary to the flow of 

 the stream. 



ground from the quarry on. Figures 19 to 24 show the irregularity 

 of the limestone underlying the stream bed. These layers are inter- 

 spersed with fossils such as are shown in figure 22. It is belie /ed 

 that the water dissolves the softer limestone and these harder fos- 

 sils prevent the harder layers from settling together. This causes 

 numerous large underground waterways. The water evidently set- 

 tles through these until it strikes some harder, more continuous 

 layer or until it encounters some strata of finer material which pre- 

 vent the rapid passage of the water. At any rate, the water does 

 not come to the surface again. Near the river end of the course of 

 Dry Run about two miles from the quarry a number of springs rise, 

 as shown in figures 25 and 26. Undoubtedly these springs are not 



