592 



IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



An Irregular Soluti&n Surface on the G^ypsuni. — The overbur- 

 den of grlacial drift at the Vincent clay pit is removed by hy- 

 draulicking. The o:ypsum, which here has a maximum thickness 

 of about seven feet, is then broken up and removed. In the fall 

 of 1917 (luite a large area had been cleared of drift and a re- 

 markably irregular surface of the (gypsum was revealed. From 

 its nature it is evident that the in'e.uularity was caused by aque- 

 ous solution or erosion rather than by ice erosion. Sinuous wind- 

 ing- channels have been cut almost through the gypsum bed as the 



Fig. 199.- 

 well shown. 



-A detail of the irregular surface in the gypsum. 

 Vincent pit. 



The baniling is 



accompanying views show. What was apparently a larger chan- 

 nel extended almost the entire length of the stripping (see figure 

 196). Pinnacles and towers and walls of fantastic design have 

 been carved in the solid rock and a most picturesque miniature 

 topography has been formed. Potholes or pothole-like cavities 

 have been dissolved out where we may imagine that the tiny tor- 

 rents dashed and swirled or the slowly percolating waters of a 

 bygone day seeped among the rocks and clays that formed the 

 surface of that time. 



