8 FIELD OPERATION'S OF THE BUEEAU OF SOILS, 1918. 



is supposed that these depressions are vestiges of the channel held 

 by the Mississippi River at the time of the Illinoian glaciation, when 

 the river followed the western edge of the ice sheet. Another notice- 

 able feature of the western upland is two more or less pronounced 

 swells lying east of and roughly paralleling the depression just de- 

 scribed. These are each about 1 mile wide. In sees. 17, 18, and 21, 

 T. 73 N., R. 3 W., are a few small sinkholes, about 20 feet deep and 

 5 to 8 rods wide, due to holes or caverns in the underlying limestone. 



The highest point in the county is in the southeastern part of 

 Morning Sun Township, where an elevation of nearly 900 feet above 

 sea level is reached. The elevation at Port Louisa, on the Missis- 

 sippi River, in the eastern part of the county, taken at mean low 

 water is 526 feet, while across the river at Keithsburg, 111., If miles 

 north of the southern boundary of the county, the elevation is 523 feet. 



The eastern upland, with the exception of about 12 square miles, 

 drains into the j owa River. The divide between the Iowa and Mis- 

 sissippi Rivers follows the Mississippi bluffs in Jefferson and Port 

 Louisa Townships, north of which it turns back and runs about 2 

 miles west of the bluffs. The eastern slope is drained by short, 

 V-shaped gulches and ravines, often v/ith precipitous slopes. Only 

 two streams of any length occur. These are in (}randview Town- 

 ship, the northern one being known as Whisky Run. The western 

 slope is drained by longer watercourses, with more rounded and 

 gentler valley walls. The fall of the highland from east to west, 

 with the exception of the northern part, where it is less, is 20 feet 

 per mile. Several main creeks, the largest of which is Indian Creek, 

 have developed. This stream has a bottom land one-eighth to one- 

 fourth mile in width. 



The drainage of the western upland, with the exception of the 

 southwest half of T. 73 N., R.-l W., and the extreme southwestern cor- 

 ner of Elm Grove Township, which drain west and eventually into the 

 Skunk River, is tributary to the Iowa River. In the southern tier 

 of townships the streams run in a general northerly direction, wliile 

 over the remainder of the eastern slope the general direction is east. 

 Some of the north-flowing creeks have their beds partly in limestone, 

 and here their valleys become relatively narrow. 



In both the eastern and western drift plains, with the exception 

 of a few small level areas, ample surface drainage is afforded by 

 widely ramifying branches and streamlets. Even in the level areas 

 there is probably no farm without a natural drainage outlet. The 

 terraces are for the most part sufficiently tlrained for cultivation. 

 In sandy areas the rain water readily soaks into the ground. Where 

 the soil is heavier and underlain by a heavy substratum, the run-off 

 is usually taken care of by tile and ditches connecting with the 



